streams

This module provides a stream interface and two implementations thereof: the FileStream and the StringStream which implement the stream interface for Nim file objects (File) and strings.

Other modules may provide other implementations for this standard stream interface.

Basic usage

The basic flow of using this module is:

1. Open input stream
2. Read or write stream
3. Close stream

StringStream example

import streams

var strm = newStringStream("""The first line
the second line
the third line""")

var line = ""

while strm.readLine(line):
  echo line

# Output:
# The first line
# the second line
# the third line

strm.close()

FileStream example

Write file stream example:

import streams

var strm = newFileStream("somefile.txt", fmWrite)
var line = ""

if not isNil(strm):
  strm.writeLine("The first line")
  strm.writeLine("the second line")
  strm.writeLine("the third line")
  strm.close()

# Output (somefile.txt):
# The first line
# the second line
# the third line

Read file stream example:

import streams

var strm = newFileStream("somefile.txt", fmRead)
var line = ""

if not isNil(strm):
  while strm.readLine(line):
    echo line
  strm.close()

# Output:
# The first line
# the second line
# the third line

See also

• asyncstreams module
• io module for FileMode enum

Imports

since

Types

Stream = ref StreamObj

All procedures of this module use this type. Procedures don't directly use StreamObj. Source Edit

StreamObj = object of RootObj
  closeImpl*: proc (s: Stream) {...}{.nimcall, raises: [Exception, IOError, OSError],
                                 tags: [WriteIOEffect], gcsafe.}
  atEndImpl*: proc (s: Stream): bool {...}{.nimcall,
                                       raises: [Defect, IOError, OSError],
                                       tags: [], gcsafe.}
  setPositionImpl*: proc (s: Stream; pos: int) {...}{.nimcall,
      raises: [Defect, IOError, OSError], tags: [], gcsafe.}
  getPositionImpl*: proc (s: Stream): int {...}{.nimcall,
      raises: [Defect, IOError, OSError], tags: [], gcsafe.}
  readDataStrImpl*: proc (s: Stream; buffer: var string; slice: Slice[int]): int {...}{.
      nimcall, raises: [Defect, IOError, OSError], tags: [ReadIOEffect], gcsafe.}
  readLineImpl*: proc (s: Stream; line: var TaintedString): bool {...}{.nimcall,
      raises: [Defect, IOError, OSError], tags: [ReadIOEffect], gcsafe.}
  readDataImpl*: proc (s: Stream; buffer: pointer; bufLen: int): int {...}{.nimcall,
      raises: [Defect, IOError, OSError], tags: [ReadIOEffect], gcsafe.}
  peekDataImpl*: proc (s: Stream; buffer: pointer; bufLen: int): int {...}{.nimcall,
      raises: [Defect, IOError, OSError], tags: [ReadIOEffect], gcsafe.}
  writeDataImpl*: proc (s: Stream; buffer: pointer; bufLen: int) {...}{.nimcall,
      raises: [Defect, IOError, OSError], tags: [WriteIOEffect], gcsafe.}
  flushImpl*: proc (s: Stream) {...}{.nimcall, raises: [Defect, IOError, OSError],
                                 tags: [WriteIOEffect], gcsafe.}

Stream interface that supports writing or reading.

Note:

• That these fields here shouldn't be used directly. They are accessible so that a stream implementation can override them.

Source Edit

StringStream = ref StringStreamObj

A stream that encapsulates a string. Source Edit

StringStreamObj = object of StreamObj
  data*: string              ## A string data.
                             ## This is updated when called `writeLine` etc.
  pos: int

A string stream object. Source Edit

FileStream = ref FileStreamObj

A stream that encapsulates a File.

Note: Not available for JS backend.

Source Edit

FileStreamObj = object of Stream
  f: File

A file stream object.

Note: Not available for JS backend.

Source Edit

Procs

proc flush(s: Stream) {...}{.raises: [IOError, OSError], tags: [WriteIOEffect].}

Flushes the buffers that the stream s might use.

This procedure causes any unwritten data for that stream to be delivered to the host environment to be written to the file.

See also:

• close proc

Example:

from os import removeFile

var strm = newFileStream("somefile.txt", fmWrite)

doAssert "Before write:" & readFile("somefile.txt") == "Before write:"
strm.write("hello")
doAssert "After  write:" & readFile("somefile.txt") == "After  write:"

strm.flush()
doAssert "After  flush:" & readFile("somefile.txt") == "After  flush:hello"
strm.write("HELLO")
strm.flush()
doAssert "After  flush:" & readFile("somefile.txt") == "After  flush:helloHELLO"

strm.close()
doAssert "After  close:" & readFile("somefile.txt") == "After  close:helloHELLO"
removeFile("somefile.txt")

Source Edit

proc close(s: Stream) {...}{.raises: [Exception, IOError, OSError],
                        tags: [WriteIOEffect].}

Closes the stream s.

See also:

• flush proc

Example:

var strm = newStringStream("The first line\nthe second line\nthe third line")
## do something...
strm.close()

Source Edit

proc atEnd(s: Stream): bool {...}{.raises: [IOError, OSError], tags: [].}

Checks if more data can be read from s. Returns true if all data has been read.

Example:

var strm = newStringStream("The first line\nthe second line\nthe third line")
var line = ""
doAssert strm.atEnd() == false
while strm.readLine(line):
  discard
doAssert strm.atEnd() == true
strm.close()

Source Edit

proc setPosition(s: Stream; pos: int) {...}{.raises: [IOError, OSError], tags: [].}

Sets the position pos of the stream s.

Example:

var strm = newStringStream("The first line\nthe second line\nthe third line")
strm.setPosition(4)
doAssert strm.readLine() == "first line"
strm.setPosition(0)
doAssert strm.readLine() == "The first line"
strm.close()

Source Edit

proc getPosition(s: Stream): int {...}{.raises: [IOError, OSError], tags: [].}

Retrieves the current position in the stream s.

Example:

var strm = newStringStream("The first line\nthe second line\nthe third line")
doAssert strm.getPosition() == 0
discard strm.readLine()
doAssert strm.getPosition() == 15
strm.close()

Source Edit

proc readData(s: Stream; buffer: pointer; bufLen: int): int {...}{.
    raises: [IOError, OSError], tags: [ReadIOEffect].}

Low level proc that reads data into an untyped buffer of bufLen size.

JS note: buffer is treated as a ptr string and written to between 0..<bufLen.

Example:

var strm = newStringStream("abcde")
var buffer: array[6, char]
doAssert strm.readData(addr(buffer), 1024) == 5
doAssert buffer == ['a', 'b', 'c', 'd', 'e', '\x00']
doAssert strm.atEnd() == true
strm.close()

Source Edit

proc readDataStr(s: Stream; buffer: var string; slice: Slice[int]): int {...}{.
    raises: [IOError, OSError], tags: [ReadIOEffect].}

Low level proc that reads data into a string buffer at slice.

Example:

var strm = newStringStream("abcde")
var buffer = "12345"
doAssert strm.readDataStr(buffer, 0..3) == 4
doAssert buffer == "abcd5"
strm.close()

Source Edit

proc readAll(s: Stream): string {...}{.raises: [IOError, OSError],
                                  tags: [ReadIOEffect].}

Reads all available data.

Example:

var strm = newStringStream("The first line\nthe second line\nthe third line")
doAssert strm.readAll() == "The first line\nthe second line\nthe third line"
doAssert strm.atEnd() == true
strm.close()

Source Edit

proc peekData(s: Stream; buffer: pointer; bufLen: int): int {...}{.
    raises: [IOError, OSError], tags: [ReadIOEffect].}

Low level proc that reads data into an untyped buffer of bufLen size without moving stream position.

JS note: buffer is treated as a ptr string and written to between 0..<bufLen.

Example:

var strm = newStringStream("abcde")
var buffer: array[6, char]
doAssert strm.peekData(addr(buffer), 1024) == 5
doAssert buffer == ['a', 'b', 'c', 'd', 'e', '\x00']
doAssert strm.atEnd() == false
strm.close()

Source Edit

proc writeData(s: Stream; buffer: pointer; bufLen: int) {...}{.
    raises: [IOError, OSError], tags: [WriteIOEffect].}

Low level proc that writes an untyped buffer of bufLen size to the stream s.

JS note: buffer is treated as a ptr string and read between 0..<bufLen.

Example:

## writeData
var strm = newStringStream("")
var buffer = ['a', 'b', 'c', 'd', 'e']
strm.writeData(addr(buffer), sizeof(buffer))
doAssert strm.atEnd() == true
## readData
strm.setPosition(0)
var buffer2: array[6, char]
doAssert strm.readData(addr(buffer2), sizeof(buffer2)) == 5
doAssert buffer2 == ['a', 'b', 'c', 'd', 'e', '\x00']
strm.close()

Source Edit

proc write[T](s: Stream; x: T)

Generic write procedure. Writes x to the stream s. Implementation:

Note: Not available for JS backend. Use write(Stream, string) for now.

s.writeData(s, unsafeAddr(x), sizeof(x))

Example:

var strm = newStringStream("")
strm.write("abcde")
strm.setPosition(0)
doAssert strm.readAll() == "abcde"
strm.close()

Source Edit

proc write(s: Stream; x: string) {...}{.raises: [IOError, OSError],
                                   tags: [WriteIOEffect].}

Writes the string x to the the stream s. No length field or terminating zero is written.

Example:

var strm = newStringStream("")
strm.write("THE FIRST LINE")
strm.setPosition(0)
doAssert strm.readLine() == "THE FIRST LINE"
strm.close()

Source Edit

proc write(s: Stream; args: varargs[string, `$`]) {...}{.raises: [IOError, OSError],
    tags: [WriteIOEffect].}

Writes one or more strings to the the stream. No length fields or terminating zeros are written.

Example:

var strm = newStringStream("")
strm.write(1, 2, 3, 4)
strm.setPosition(0)
doAssert strm.readLine() == "1234"
strm.close()

Source Edit

proc writeLine(s: Stream; args: varargs[string, `$`]) {...}{.
    raises: [IOError, OSError], tags: [WriteIOEffect].}

Writes one or more strings to the the stream s followed by a new line. No length field or terminating zero is written.

Example:

var strm = newStringStream("")
strm.writeLine(1, 2)
strm.writeLine(3, 4)
strm.setPosition(0)
doAssert strm.readAll() == "12\n34\n"
strm.close()

Source Edit

proc read[T](s: Stream; result: var T)

Generic read procedure. Reads result from the stream s.

Note: Not available for JS backend. Use readStr for now.

Example:

var strm = newStringStream("012")
## readInt
var i: int8
strm.read(i)
doAssert i == 48
## readData
var buffer: array[2, char]
strm.read(buffer)
doAssert buffer == ['1', '2']
strm.close()

Source Edit

proc peek[T](s: Stream; result: var T)

Generic peek procedure. Peeks result from the stream s.

Note: Not available for JS backend. Use peekStr for now.

Example:

var strm = newStringStream("012")
## peekInt
var i: int8
strm.peek(i)
doAssert i == 48
## peekData
var buffer: array[2, char]
strm.peek(buffer)
doAssert buffer == ['0', '1']
strm.close()

Source Edit

proc readChar(s: Stream): char {...}{.raises: [IOError, OSError],
                                 tags: [ReadIOEffect].}

Reads a char from the stream s.

Raises IOError if an error occurred. Returns '\0' as an EOF marker.

Example:

var strm = newStringStream("12\n3")
doAssert strm.readChar() == '1'
doAssert strm.readChar() == '2'
doAssert strm.readChar() == '\n'
doAssert strm.readChar() == '3'
doAssert strm.readChar() == '\x00'
strm.close()

Source Edit

proc peekChar(s: Stream): char {...}{.raises: [IOError, OSError],
                                 tags: [ReadIOEffect].}

Peeks a char from the stream s. Raises IOError if an error occurred. Returns '\0' as an EOF marker.

Example:

var strm = newStringStream("12\n3")
doAssert strm.peekChar() == '1'
doAssert strm.peekChar() == '1'
discard strm.readAll()
doAssert strm.peekChar() == '\x00'
strm.close()

Source Edit

proc readBool(s: Stream): bool {...}{.raises: [IOError, OSError],
                                 tags: [ReadIOEffect].}

Reads a bool from the stream s.

A bool is one byte long and it is true for every non-zero (0000_0000) value. Raises IOError if an error occurred.

Note: Not available for JS backend. Use readStr for now.

Example:

var strm = newStringStream()
## setup for reading data
strm.write(true)
strm.write(false)
strm.flush()
strm.setPosition(0)
## get data
doAssert strm.readBool() == true
doAssert strm.readBool() == false
doAssertRaises(IOError): discard strm.readBool()
strm.close()

Source Edit

proc peekBool(s: Stream): bool {...}{.raises: [IOError, OSError],
                                 tags: [ReadIOEffect].}

Peeks a bool from the stream s.

A bool is one byte long and it is true for every non-zero (0000_0000) value. Raises IOError if an error occurred.

Note: Not available for JS backend. Use peekStr for now.

Example:

var strm = newStringStream()
## setup for reading data
strm.write(true)
strm.write(false)
strm.flush()
strm.setPosition(0)
## get data
doAssert strm.peekBool() == true
## not false
doAssert strm.peekBool() == true
doAssert strm.readBool() == true
doAssert strm.peekBool() == false
strm.close()

Source Edit

proc readInt8(s: Stream): int8 {...}{.raises: [IOError, OSError],
                                 tags: [ReadIOEffect].}

Reads an int8 from the stream s. Raises IOError if an error occurred.

Note: Not available for JS backend. Use readStr for now.

Example:

var strm = newStringStream()
## setup for reading data
strm.write(1'i8)
strm.write(2'i8)
strm.flush()
strm.setPosition(0)
## get data
doAssert strm.readInt8() == 1'i8
doAssert strm.readInt8() == 2'i8
doAssertRaises(IOError): discard strm.readInt8()
strm.close()

Source Edit

proc peekInt8(s: Stream): int8 {...}{.raises: [IOError, OSError],
                                 tags: [ReadIOEffect].}

Peeks an int8 from the stream s. Raises IOError if an error occurred.

Note: Not available for JS backend. Use peekStr for now.

Example:

var strm = newStringStream()
## setup for reading data
strm.write(1'i8)
strm.write(2'i8)
strm.flush()
strm.setPosition(0)
## get data
doAssert strm.peekInt8() == 1'i8
## not 2'i8
doAssert strm.peekInt8() == 1'i8
doAssert strm.readInt8() == 1'i8
doAssert strm.peekInt8() == 2'i8
strm.close()

Source Edit

proc readInt16(s: Stream): int16 {...}{.raises: [IOError, OSError],
                                   tags: [ReadIOEffect].}

Reads an int16 from the stream s. Raises IOError if an error occurred.

Note: Not available for JS backend. Use readStr for now.

Example:

var strm = newStringStream()
## setup for reading data
strm.write(1'i16)
strm.write(2'i16)
strm.flush()
strm.setPosition(0)
## get data
doAssert strm.readInt16() == 1'i16
doAssert strm.readInt16() == 2'i16
doAssertRaises(IOError): discard strm.readInt16()
strm.close()

Source Edit

proc peekInt16(s: Stream): int16 {...}{.raises: [IOError, OSError],
                                   tags: [ReadIOEffect].}

Peeks an int16 from the stream s. Raises IOError if an error occurred.

Note: Not available for JS backend. Use peekStr for now.

Example:

var strm = newStringStream()
## setup for reading data
strm.write(1'i16)
strm.write(2'i16)
strm.flush()
strm.setPosition(0)
## get data
doAssert strm.peekInt16() == 1'i16
## not 2'i16
doAssert strm.peekInt16() == 1'i16
doAssert strm.readInt16() == 1'i16
doAssert strm.peekInt16() == 2'i16
strm.close()

Source Edit

proc readInt32(s: Stream): int32 {...}{.raises: [IOError, OSError],
                                   tags: [ReadIOEffect].}

Reads an int32 from the stream s. Raises IOError if an error occurred.

Note: Not available for JS backend. Use readStr for now.

Example:

var strm = newStringStream()
## setup for reading data
strm.write(1'i32)
strm.write(2'i32)
strm.flush()
strm.setPosition(0)
## get data
doAssert strm.readInt32() == 1'i32
doAssert strm.readInt32() == 2'i32
doAssertRaises(IOError): discard strm.readInt32()
strm.close()

Source Edit

proc peekInt32(s: Stream): int32 {...}{.raises: [IOError, OSError],
                                   tags: [ReadIOEffect].}

Peeks an int32 from the stream s. Raises IOError if an error occurred.

Note: Not available for JS backend. Use peekStr for now.

Example:

var strm = newStringStream()
## setup for reading data
strm.write(1'i32)
strm.write(2'i32)
strm.flush()
strm.setPosition(0)
## get data
doAssert strm.peekInt32() == 1'i32
## not 2'i32
doAssert strm.peekInt32() == 1'i32
doAssert strm.readInt32() == 1'i32
doAssert strm.peekInt32() == 2'i32
strm.close()

Source Edit

proc readInt64(s: Stream): int64 {...}{.raises: [IOError, OSError],
                                   tags: [ReadIOEffect].}

Reads an int64 from the stream s. Raises IOError if an error occurred.

Note: Not available for JS backend. Use readStr for now.

Example:

var strm = newStringStream()
## setup for reading data
strm.write(1'i64)
strm.write(2'i64)
strm.flush()
strm.setPosition(0)
## get data
doAssert strm.readInt64() == 1'i64
doAssert strm.readInt64() == 2'i64
doAssertRaises(IOError): discard strm.readInt64()
strm.close()

Source Edit

proc peekInt64(s: Stream): int64 {...}{.raises: [IOError, OSError],
                                   tags: [ReadIOEffect].}

Peeks an int64 from the stream s. Raises IOError if an error occurred.

Note: Not available for JS backend. Use peekStr for now.

Example:

var strm = newStringStream()
## setup for reading data
strm.write(1'i64)
strm.write(2'i64)
strm.flush()
strm.setPosition(0)
## get data
doAssert strm.peekInt64() == 1'i64
## not 2'i64
doAssert strm.peekInt64() == 1'i64
doAssert strm.readInt64() == 1'i64
doAssert strm.peekInt64() == 2'i64
strm.close()

Source Edit

proc readUint8(s: Stream): uint8 {...}{.raises: [IOError, OSError],
                                   tags: [ReadIOEffect].}

Reads an uint8 from the stream s. Raises IOError if an error occurred.

Note: Not available for JS backend. Use readStr for now.

Example:

var strm = newStringStream()
## setup for reading data
strm.write(1'u8)
strm.write(2'u8)
strm.flush()
strm.setPosition(0)
## get data
doAssert strm.readUint8() == 1'u8
doAssert strm.readUint8() == 2'u8
doAssertRaises(IOError): discard strm.readUint8()
strm.close()

Source Edit

proc peekUint8(s: Stream): uint8 {...}{.raises: [IOError, OSError],
                                   tags: [ReadIOEffect].}

Peeks an uint8 from the stream s. Raises IOError if an error occurred.

Note: Not available for JS backend. Use peekStr for now.

Example:

var strm = newStringStream()
## setup for reading data
strm.write(1'u8)
strm.write(2'u8)
strm.flush()
strm.setPosition(0)
## get data
doAssert strm.peekUint8() == 1'u8
## not 2'u8
doAssert strm.peekUint8() == 1'u8
doAssert strm.readUint8() == 1'u8
doAssert strm.peekUint8() == 2'u8
strm.close()

Source Edit

proc readUint16(s: Stream): uint16 {...}{.raises: [IOError, OSError],
                                     tags: [ReadIOEffect].}

Reads an uint16 from the stream s. Raises IOError if an error occurred.

Note: Not available for JS backend. Use readStr for now.

Example:

var strm = newStringStream()
## setup for reading data
strm.write(1'u16)
strm.write(2'u16)
strm.flush()
strm.setPosition(0)
## get data
doAssert strm.readUint16() == 1'u16
doAssert strm.readUint16() == 2'u16
doAssertRaises(IOError): discard strm.readUint16()
strm.close()

Source Edit

proc peekUint16(s: Stream): uint16 {...}{.raises: [IOError, OSError],
                                     tags: [ReadIOEffect].}

Peeks an uint16 from the stream s. Raises IOError if an error occurred.

Note: Not available for JS backend. Use peekStr for now.

Example:

var strm = newStringStream()
## setup for reading data
strm.write(1'u16)
strm.write(2'u16)
strm.flush()
strm.setPosition(0)
## get data
doAssert strm.peekUint16() == 1'u16
## not 2'u16
doAssert strm.peekUint16() == 1'u16
doAssert strm.readUint16() == 1'u16
doAssert strm.peekUint16() == 2'u16
strm.close()

Source Edit

proc readUint32(s: Stream): uint32 {...}{.raises: [IOError, OSError],
                                     tags: [ReadIOEffect].}

Reads an uint32 from the stream s. Raises IOError if an error occurred.

Note: Not available for JS backend. Use readStr for now.

Example:

var strm = newStringStream()
## setup for reading data
strm.write(1'u32)
strm.write(2'u32)
strm.flush()
strm.setPosition(0)

## get data
doAssert strm.readUint32() == 1'u32
doAssert strm.readUint32() == 2'u32
doAssertRaises(IOError): discard strm.readUint32()
strm.close()

Source Edit

proc peekUint32(s: Stream): uint32 {...}{.raises: [IOError, OSError],
                                     tags: [ReadIOEffect].}

Peeks an uint32 from the stream s. Raises IOError if an error occurred.

Note: Not available for JS backend. Use peekStr for now.

Example:

var strm = newStringStream()
## setup for reading data
strm.write(1'u32)
strm.write(2'u32)
strm.flush()
strm.setPosition(0)
## get data
doAssert strm.peekUint32() == 1'u32
## not 2'u32
doAssert strm.peekUint32() == 1'u32
doAssert strm.readUint32() == 1'u32
doAssert strm.peekUint32() == 2'u32
strm.close()

Source Edit

proc readUint64(s: Stream): uint64 {...}{.raises: [IOError, OSError],
                                     tags: [ReadIOEffect].}

Reads an uint64 from the stream s. Raises IOError if an error occurred.

Note: Not available for JS backend. Use readStr for now.

Example:

var strm = newStringStream()
## setup for reading data
strm.write(1'u64)
strm.write(2'u64)
strm.flush()
strm.setPosition(0)
## get data
doAssert strm.readUint64() == 1'u64
doAssert strm.readUint64() == 2'u64
doAssertRaises(IOError): discard strm.readUint64()
strm.close()

Source Edit

proc peekUint64(s: Stream): uint64 {...}{.raises: [IOError, OSError],
                                     tags: [ReadIOEffect].}

Peeks an uint64 from the stream s. Raises IOError if an error occurred.

Note: Not available for JS backend. Use peekStr for now.

Example:

var strm = newStringStream()
## setup for reading data
strm.write(1'u64)
strm.write(2'u64)
strm.flush()
strm.setPosition(0)
## get data
doAssert strm.peekUint64() == 1'u64
## not 2'u64
doAssert strm.peekUint64() == 1'u64
doAssert strm.readUint64() == 1'u64
doAssert strm.peekUint64() == 2'u64
strm.close()

Source Edit

proc readFloat32(s: Stream): float32 {...}{.raises: [IOError, OSError],
                                       tags: [ReadIOEffect].}

Reads a float32 from the stream s. Raises IOError if an error occurred.

Note: Not available for JS backend. Use readStr for now.

Example:

var strm = newStringStream()
## setup for reading data
strm.write(1'f32)
strm.write(2'f32)
strm.flush()
strm.setPosition(0)
## get data
doAssert strm.readFloat32() == 1'f32
doAssert strm.readFloat32() == 2'f32
doAssertRaises(IOError): discard strm.readFloat32()
strm.close()

Source Edit

proc peekFloat32(s: Stream): float32 {...}{.raises: [IOError, OSError],
                                       tags: [ReadIOEffect].}

Peeks a float32 from the stream s. Raises IOError if an error occurred.

Note: Not available for JS backend. Use peekStr for now.

Example:

var strm = newStringStream()
## setup for reading data
strm.write(1'f32)
strm.write(2'f32)
strm.flush()
strm.setPosition(0)
## get data
doAssert strm.peekFloat32() == 1'f32
## not 2'f32
doAssert strm.peekFloat32() == 1'f32
doAssert strm.readFloat32() == 1'f32
doAssert strm.peekFloat32() == 2'f32
strm.close()

Source Edit

proc readFloat64(s: Stream): float64 {...}{.raises: [IOError, OSError],
                                       tags: [ReadIOEffect].}

Reads a float64 from the stream s. Raises IOError if an error occurred.

Note: Not available for JS backend. Use readStr for now.

Example:

var strm = newStringStream()
## setup for reading data
strm.write(1'f64)
strm.write(2'f64)
strm.flush()
strm.setPosition(0)
## get data
doAssert strm.readFloat64() == 1'f64
doAssert strm.readFloat64() == 2'f64
doAssertRaises(IOError): discard strm.readFloat64()
strm.close()

Source Edit

proc peekFloat64(s: Stream): float64 {...}{.raises: [IOError, OSError],
                                       tags: [ReadIOEffect].}

Peeks a float64 from the stream s. Raises IOError if an error occurred.

Note: Not available for JS backend. Use peekStr for now.

Example:

var strm = newStringStream()
## setup for reading data
strm.write(1'f64)
strm.write(2'f64)
strm.flush()
strm.setPosition(0)
## get data
doAssert strm.peekFloat64() == 1'f64
## not 2'f64
doAssert strm.peekFloat64() == 1'f64
doAssert strm.readFloat64() == 1'f64
doAssert strm.peekFloat64() == 2'f64
strm.close()

Source Edit

proc readStr(s: Stream; length: int; str: var TaintedString) {...}{.
    raises: [IOError, OSError], tags: [ReadIOEffect].}

Reads a string of length length from the stream s. Raises IOError if an error occurred. Source Edit

proc readStr(s: Stream; length: int): TaintedString {...}{.
    raises: [IOError, OSError], tags: [ReadIOEffect].}

Reads a string of length length from the stream s. Raises IOError if an error occurred.

Example:

var strm = newStringStream("abcde")
doAssert strm.readStr(2) == "ab"
doAssert strm.readStr(2) == "cd"
doAssert strm.readStr(2) == "e"
doAssert strm.readStr(2) == ""
strm.close()

Source Edit

proc peekStr(s: Stream; length: int; str: var TaintedString) {...}{.
    raises: [IOError, OSError], tags: [ReadIOEffect].}

Peeks a string of length length from the stream s. Raises IOError if an error occurred. Source Edit

proc peekStr(s: Stream; length: int): TaintedString {...}{.
    raises: [IOError, OSError], tags: [ReadIOEffect].}

Peeks a string of length length from the stream s. Raises IOError if an error occurred.

Example:

var strm = newStringStream("abcde")
doAssert strm.peekStr(2) == "ab"
## not "cd
doAssert strm.peekStr(2) == "ab"
doAssert strm.readStr(2) == "ab"
doAssert strm.peekStr(2) == "cd"
strm.close()

Source Edit

proc readLine(s: Stream; line: var TaintedString): bool {...}{.
    raises: [IOError, OSError], tags: [ReadIOEffect].}

Reads a line of text from the stream s into line. line must not be nil! May throw an IO exception.

A line of text may be delimited by LF or CRLF. The newline character(s) are not part of the returned string. Returns false if the end of the file has been reached, true otherwise. If false is returned line contains no new data.

See also:

• readLine(Stream) proc
• peekLine(Stream) proc
• peekLine(Stream, TaintedString) proc

Example:

var strm = newStringStream("The first line\nthe second line\nthe third line")
var line = ""
doAssert strm.readLine(line) == true
doAssert line == "The first line"
doAssert strm.readLine(line) == true
doAssert line == "the second line"
doAssert strm.readLine(line) == true
doAssert line == "the third line"
doAssert strm.readLine(line) == false
doAssert line == ""
strm.close()

Source Edit

proc peekLine(s: Stream; line: var TaintedString): bool {...}{.
    raises: [IOError, OSError], tags: [ReadIOEffect].}

Peeks a line of text from the stream s into line. line must not be nil! May throw an IO exception.

A line of text may be delimited by CR, LF or CRLF. The newline character(s) are not part of the returned string. Returns false if the end of the file has been reached, true otherwise. If false is returned line contains no new data.

See also:

• readLine(Stream) proc
• readLine(Stream, TaintedString) proc
• peekLine(Stream) proc

Example:

var strm = newStringStream("The first line\nthe second line\nthe third line")
var line = ""
doAssert strm.peekLine(line) == true
doAssert line == "The first line"
doAssert strm.peekLine(line) == true
## not "the second line"
doAssert line == "The first line"
doAssert strm.readLine(line) == true
doAssert line == "The first line"
doAssert strm.peekLine(line) == true
doAssert line == "the second line"
strm.close()

Source Edit

proc readLine(s: Stream): TaintedString {...}{.raises: [IOError, OSError],
    tags: [ReadIOEffect].}

Reads a line from a stream s. Raises IOError if an error occurred.

Note: This is not very efficient.

See also:

• readLine(Stream, TaintedString) proc
• peekLine(Stream) proc
• peekLine(Stream, TaintedString) proc

Example:

var strm = newStringStream("The first line\nthe second line\nthe third line")
doAssert strm.readLine() == "The first line"
doAssert strm.readLine() == "the second line"
doAssert strm.readLine() == "the third line"
doAssertRaises(IOError): discard strm.readLine()
strm.close()

Source Edit

proc peekLine(s: Stream): TaintedString {...}{.raises: [IOError, OSError],
    tags: [ReadIOEffect].}

Peeks a line from a stream s. Raises IOError if an error occurred.

Note: This is not very efficient.

See also:

• readLine(Stream) proc
• readLine(Stream, TaintedString) proc
• peekLine(Stream, TaintedString) proc

Example:

var strm = newStringStream("The first line\nthe second line\nthe third line")
doAssert strm.peekLine() == "The first line"
## not "the second line"
doAssert strm.peekLine() == "The first line"
doAssert strm.readLine() == "The first line"
doAssert strm.peekLine() == "the second line"
strm.close()

Source Edit

proc newStringStream(s: string = ""): owned StringStream {...}{.raises: [], tags: [].}

Creates a new stream from the string s.

See also:

• newFileStream proc creates a file stream from opened File.
• newFileStream proc creates a file stream from the file name and the mode.
• openFileStream proc creates a file stream from the file name and the mode.

Example:

var strm = newStringStream("The first line\nthe second line\nthe third line")
doAssert strm.readLine() == "The first line"
doAssert strm.readLine() == "the second line"
doAssert strm.readLine() == "the third line"
strm.close()

Source Edit

proc newFileStream(f: File): owned FileStream {...}{.raises: [], tags: [].}

Creates a new stream from the file f.

Note: Not available for JS backend.

See also:

• newStringStream proc creates a new stream from string.
• newFileStream proc is the same as using open proc on Examples.
• openFileStream proc creates a file stream from the file name and the mode.

Example:

## Input (somefile.txt):
## The first line
## the second line
## the third line
var f: File
if open(f, "somefile.txt", fmRead, -1):
  var strm = newFileStream(f)
  var line = ""
  while strm.readLine(line):
    echo line
  ## Output:
  ## The first line
  ## the second line
  ## the third line
  strm.close()

Source Edit

proc newFileStream(filename: string; mode: FileMode = fmRead; bufSize: int = -1): owned
    FileStream {...}{.raises: [], tags: [].}

Creates a new stream from the file named filename with the mode mode.

If the file cannot be opened, nil is returned. See the io module for a list of available FileMode enums.

Note:

• This function returns nil in case of failure. To prevent unexpected behavior and ensure proper error handling, use openFileStream proc instead.
• Not available for JS backend.

See also:

• newStringStream proc creates a new stream from string.
• newFileStream proc creates a file stream from opened File.
• openFileStream proc creates a file stream from the file name and the mode.

Example:

from os import removeFile
var strm = newFileStream("somefile.txt", fmWrite)
if not isNil(strm):
  strm.writeLine("The first line")
  strm.writeLine("the second line")
  strm.writeLine("the third line")
  strm.close()
  ## Output (somefile.txt)
  ## The first line
  ## the second line
  ## the third line
  removeFile("somefile.txt")

Source Edit

proc openFileStream(filename: string; mode: FileMode = fmRead;
                    bufSize: int = -1): owned FileStream {...}{.raises: [IOError],
    tags: [].}

Creates a new stream from the file named filename with the mode mode. If the file cannot be opened, an IO exception is raised.

Note: Not available for JS backend.

See also:

• newStringStream proc creates a new stream from string.
• newFileStream proc creates a file stream from opened File.
• newFileStream proc creates a file stream from the file name and the mode.

Example:

try:
  ## Input (somefile.txt):
  ## The first line
  ## the second line
  ## the third line
  var strm = openFileStream("somefile.txt")
  echo strm.readLine()
  ## Output:
  ## The first line
  strm.close()
except:
  stderr.write getCurrentExceptionMsg()

Source Edit

Iterators

iterator lines(s: Stream): TaintedString {...}{.raises: [IOError, OSError],
    tags: [ReadIOEffect].}

Iterates over every line in the stream. The iteration is based on readLine.

See also:

• readLine(Stream) proc
• readLine(Stream, TaintedString) proc

Example:

var strm = newStringStream("The first line\nthe second line\nthe third line")
var lines: seq[string]
for line in strm.lines():
  lines.add line
doAssert lines == @["The first line", "the second line", "the third line"]
strm.close()

Source Edit