std::strstream::str

 

C++

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Feature test macros (C++20)

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Technical specifications

Symbols index

External libraries

 

Input/output library

I/O manipulators

Print functions (C++23)

C-style I/O

Buffers

basic_streambuf

basic_filebuf

basic_stringbuf

basic_spanbuf (C++23)

strstreambuf (C++98/26*)

basic_syncbuf (C++20)

Streams

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ios_base

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basic_stringstream

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basic_ispanstream (C++23)

basic_ospanstream (C++23)

basic_spanstream (C++23)

istrstream (C++98/26*)

ostrstream (C++98/26*)

strstream (C++98/26*)

Synchronized Output

basic_osyncstream (C++20)

Types

streamoff

streamsize

fpos

Error category interface

iostream_category (C++11)

io_errc (C++11)

 

std::strstream

Member functions

strstream::strstream

strstream::~strstream

strstream::rdbuf

strstream::str

strstream::pcount

strstream::freeze

 

char* str();		(deprecated in C++98) (removed in C++26)

Returns the pointer to the beginning of the buffer, after freezing it. Effectively calls rdbuf()->str().

Parameters

(none)

Return value

Pointer to the beginning of the buffer in the associated std::strstreambuf or a null pointer if no buffer is available.

Notes

Before a call to str() that uses the result as a C-string, the stream buffer must be null-terminated. Regular output such as with stream << 1.2 does not store a null terminator, it must be appended explicitly, typically with the manipulator std::ends.

After a call to str(), dynamic streams become frozen. A call to freeze(false) is required before exiting the scope in which this strstream object was created. otherwise the destructor will leak memory. Also, additional output to a frozen stream may be truncated once it reaches the end of the allocated buffer, which may leave the buffer not null-terminated.

Example

Run this code

#include <iostream>
#include <strstream>
 
int main()
{
    std::strstream dyn; // dynamically-allocated output buffer
    dyn << "Test: " << 1.23; // not adding std::ends to demonstrate append behavior
    std::cout << "The output stream holds \"";
    std::cout.write(dyn.str(), dyn.pcount()) << "\"\n"; 
    // the stream is now frozen due to str()
    dyn << " More text" << std::ends;
    std::cout << "The output stream holds \"";
    std::cout.write(dyn.str(), dyn.pcount()) << "\"\n";
    dyn.freeze(false);
}

Possible output:

The stream holds "Test: 1.23"
The stream holds "Test: 1.23 More "

See also

str	marks the buffer frozen and returns the beginning pointer of the input sequence (public member function of std::strstreambuf)