CITS2002 Systems Programming  
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Writing text output to a file

We've used fgets() to 'get' a line of text (a string) from a file;
we similarly use fputs() to 'put' (write) a line of text.

The file pointer passed to fputs() must previously have been opened for writing or appending.

Copying a text file using file pointers

We now have all the functions necessary to copy one text file to another, one line line at a time:


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

void copy_text_file(char destination[], char source[])
{
    FILE        *fp_in   = fopen(source, "r");
    FILE        *fp_out  = fopen(destination,  "w");

//  ENSURE THAT OPENING BOTH FILES HAS BEEN SUCCESSFUL
    if(fp_in != NULL && fp_out != NULL) {
        char    line[BUFSIZ];

        while( fgets(line, sizeof line, fp_in) != NULL) {  
            if(fputs(line, fp_out) == EOF) {
                printf("error copying file\n");
                exit(EXIT_FAILURE);
            }
        }
    }
//  ENSURE THAT WE ONLY CLOSE FILES THAT ARE OPEN
    if(fp_in != NULL) {
        fclose(fp_in);
    }
    if(fp_out != NULL) {
        fclose(fp_out);
    }
}

 


CITS2002 Systems Programming, Lecture 8, p8, 17th August 2021.