How Can I Write to a Memory Buffer Using a FILE* in C?

Writing to a Memory Buffer via FILE*

This question explores the possibility of creating a memory buffer as a FILE. It arises in situations where TiXml can print XML to a FILE but not directly to a memory buffer.

POSIX Solution

One solution to this problem is to utilize the POSIX functions fmemopen or open_memstream. Both functions allow the use of memory as a FILE descriptor, but they differ in semantics.

fmemopen creates a memory buffer of a specified size and associates it with a FILE stream. Data written to the FILE will be stored in the memory buffer.

open_memstream creates a pipe and associates it with a FILE stream. Data written to the FILE will be written to the pipe buffer. This approach is more suitable for situations where the size of the data is not known in advance.

Example Usage:

Here's an example using fmemopen to create a memory buffer for a FILE*:

<code class="c">#include <stdlib.h>
#include <stdio.h>
#include <string.h>

int main() {
    // Create a 1024-byte memory buffer
    char buffer[1024];
    FILE *fp = fmemopen(buffer, sizeof(buffer), "w");

    // Write some data to the buffer
    fputs("Hello, world!", fp);
    fclose(fp);

    // Read the data back from the buffer
    rewind(fp);
    char readBuffer[1024];
    fread(readBuffer, sizeof(char), 1024, fp);

    printf("%s", readBuffer);

    return 0;
}</code>

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