2.1.9.15 fwrite

Description

Writes up to count items, of size length each, from buffer to the output stream.

Syntax

size_t fwrite( const void * buffer, size_t size, size_t count, FILE * stream )

Parameters

buffer

Pointer to data to be written

size

Item size in bytes

count

Maximum number of items to be written

stream

Pointer to FILE

Return

fwrite returns the number of full items actually written, which may be less than count

if an error occurs. Also, if an error occurs, the file-position indicator cannot be determined.

Examples

EX1

//The following opens a file named fwrite.out and writes 25 characters to the file. 
//It then tries to open fwrite.out and read in 25 characters.If the attempt 
//succeeds,the program displays the number of actual items read.

void test_fwrite()
{
    FILE *stream;
    char list[30];
    int  i, numread, numwritten;
    
    // Open file in text mode:
    stream = fopen( "fwrite.out", "w+t" );
    if(stream != NULL )
    {
        for ( i = 0; i < 25; i++ )
            list[i] = (char)('z' - i);
        
        // Write 25 characters to stream 
        numwritten = fwrite( list, sizeof( char ), 25, stream );
        printf( "Wrote %d items\n", numwritten );
        fclose( stream );
    }
    else
        printf( "Problem opening the file\n" );
    
    stream = fopen( "fwrite.out", "r+t" );
    if(stream != NULL )
    {
        // Attempt to read in 25 characters 
        numread = fread( list, sizeof( char ), 25, stream );
        printf( "Number of items read = %d\n", numread );
        printf( "Contents of buffer = %.25s\n", list );
        fclose( stream );
    }
    else
        printf( "File could not be opened\n" );
}

Remark

The fwrite function writes up to count items, of size length each, from buffer to the output stream.

The file pointer associated with stream (if there is one) is incremented by the number of bytes actually written. If stream is opened in text mode, each carriage return is replaced with a carriage-return - linefeed pair. The replacement has no effect on the return value.

See Also

fread

Header to Include

origin.h

Reference