std::strstreambuf::strstreambuf (3) - Linux Manuals

std::strstreambuf::strstreambuf: std::strstreambuf::strstreambuf

NAME

std::strstreambuf::strstreambuf - std::strstreambuf::strstreambuf

Synopsis

explicit strstreambuf( std::streamsize alsize = 0 ); (until C++11)
strstreambuf() : strstreambuf(0) {} (since C++11)
explicit strstreambuf( std::streamsize alsize );
strstreambuf( void* (*palloc)(std::size_t), void (*pfree)(void*) ); (2)
strstreambuf( char* gnext, std::streamsize n, char* pbeg = 0 ); (1) (3)
strstreambuf( signed char* gnext, std::streamsize n, signed char* pbeg = 0 ); (4)
strstreambuf( unsigned char* gnext, std::streamsize n, unsigned char* pbeg = 0 ); (5)
strstreambuf( const char* gnext, std::streamsize n ); (6)
strstreambuf( const signed char* gnext, std::streamsize n); (7)
strstreambuf( const unsigned char* gnext, std::streamsize n ); (8)

1) Constructs a std::strstreambuf object: initializes the base class by calling the default constructor of std::streambuf, initializes the buffer state to "dynamic" (the buffer will be allocated as needed), initializes allocated size to the provided alsize, initializes the allocation and the deallocation functions to null (will use new[] and delete[])
2) Constructs a std::strstreambuf object: initializes the base class by calling the default constructor of std::streambuf, initializes the buffer state to "dynamic" (the buffer will be allocated as needed), initializes allocated size to unspecified value, initializes the allocation function to palloc and the deallocation function to pfree
3-5) Constructs a std::strstreambuf object in following steps:
a) Initializes the base class by calling the default constructor of std::streambuf
b) Initializes the buffer state to "constant" (the buffer is a user-provided fixed-size buffer)
c) Determines the number of elements in the user-provided array as follows: if n is greater than zero, n is used. If n is zero, std::strlen(gnext) is executed to determine the buffer size. If n is negative, INT_MAX is used.
d) Configures the std::basic_streambuf pointers as follows: If pbeg is a null pointer, calls setg(gnext, gnext, gnext + N). If pbeg is not a null pointer, executes setg(gnext, gnext, pbeg) and setp(pbeg, pbeg+N), where N is the number of elements in the array as determined earlier.
6-8) Same as strstreambuf((char*)gnext, n), except the "constant" bit is set in the buffer state bitmask (output to this buffer is not allowed)

Parameters

alsize - the initial size of the dynamically allocated buffer
palloc - pointer to user-provided allocation function
pfree - pointer to user-provided deallocation function
gnext - pointer to the start of the get area in the user-provided array
pbeg - pointer to the start of the put area in the user-provided array
n - the number of bytes in the get area (if pbeg is null) or in the put area (if pbeg is not null) of the user-provided array

Notes

These constructors are typically called by the constructors of std::strstream

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
P0935R0 C++11 default constructor was explicit made implicit

Example

// Run this code

  #include <strstream>
  #include <iostream>

  int main()
  {
      std::strstreambuf dyn; // dynamic
      std::strstream dyn_s; // equivalent stream
      dyn_s << 1.23 << std::ends;
      std::cout << dyn_s.str() << '\n';
      dyn_s.freeze(false);

      char buf[10];
      std::strstreambuf user(buf, 10, buf); // user-provided output buffer
      std::ostrstream user_s(buf, 10); // equivalent stream
      user_s << 1.23 << std::ends;
      std::cout << buf << '\n';

      std::strstreambuf lit("1 2 3", 5); // constant
      std::istrstream lit_s("1 2 3"); // equivalent stream
      int i, j, k;
      lit_s >> i >> j >> k;
      std::cout << i << ' ' << j << ' ' << k << '\n';
  }

Output:

  1.23
  1.23
  1 2 3