fwrite()

Write elements to a file

Synopsis:

#include <stdio.h>

size_t fwrite( const void* buf,
               size_t size,
               size_t num,
               FILE* fp );

Arguments:

buf

A pointer to a buffer that contains the elements that you want to write.

size

The size of each element to write.

num

The number of elements to write.

fp

The stream to which to write the elements.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The fwrite() function writes num elements of size bytes each to the stream specified by fp.

---

If you're reading and writing large amounts of data, you can improve performance by increasing the size of the internal buffer that's used for stream I/O. For more information, see “Adjusting the buffer size” in the entry for fopen().

---

Returns:

The number of complete elements successfully written; if an error occurs, this is less than num.

Errors:

If an error occurs, errno is set to indicate the type of error.

Examples:

#include <stdio.h>
#include <stdlib.h>

struct student_data {
    int student_id;
    unsigned char marks[10];
};

int main( void )
{
    FILE *fp;
    struct student_data std;
    int i;

    fp = fopen( "file", "w" );
    if( fp != NULL ) {
        std.student_id = 1001;

        for( i = 0; i < 10; i++ ) {
            std.marks[i] = (unsigned char)(85 + i);
        }

        /* write student record with marks */
        i = fwrite( &std, sizeof( struct student_data ), 1, fp );
        printf( "Successfully wrote %d records\n", i );

        fclose( fp );
        
        if( i == 1 ) {
            return EXIT_SUCCESS;
        }
    }

    return EXIT_FAILURE;
}

Classification:

ANSI, POSIX 1003.1

See also:

errno, ferror(), fopen()