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.

Note: 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

Safety:
Cancellation point	Yes
Interrupt handler	No
Signal handler	No
Thread	Yes