C/File/File Open

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Get file name from command line and open the file

<source lang="cpp">

  1. include <stdio.h>
  2. include <stdlib.h>

int main(void) {

 FILE *fp;
 char fname[128];
 printf("Enter filename: ");
 gets(fname);
 if((fp=fopen(fname, "r"))==NULL) {
   printf("Cannot open file.\n");
   exit(1);
 }
 fclose(fp);
 return 0;

}


      </source>


Open a file and close it

<source lang="cpp">

  1. include <stdio.h>
  2. include <stdlib.h>

int main(void) {

 FILE *fp;
 if((fp = fopen("test", "rb")) == NULL) {
   printf("Cannot open file.\n");
   exit(1);
 }
 if( fclose( fp )) 
     printf("File close error.\n");
 return 0;

}


      </source>


Open a file for read

<source lang="cpp">

  1. include "stdio.h"

int main() {

   FILE *fp;
   
   int letter;
   if( ( fp = fopen( "my.txt", "r")) == NULL) {
       puts("Cannot oepn the file");
       exit( 0 );
   }
   while( ( letter = fgetc( fp ) ) != EOF)
       printf("%c",letter);
   fclose(fp);

}


      </source>


Open a file: how to use fopen

<source lang="cpp">

  1. include <stdio.h>

int main () {

 FILE *file;
 file = fopen ("my.txt","wt");
 
 if (file!=NULL)
 {
   fputs ("Hiiiiiiiiiiiii",file);
   fclose (file);
 }
 return 0;

}

      </source>


Reopen a file

<source lang="cpp">

  1. include <stdio.h>

int main(void) {

 char str[80];
 freopen("OUTPUT", "w", stdout);
 printf("Enter a string: ");
 gets(str);
 printf(str);
 return 0;

}


      </source>


Reopen a stream with a different file and mode: how to use freopen

<source lang="cpp">

  1. include <stdio.h>

int main () {

 freopen ("my.txt","w",stdout);
 printf ("This line is redirected to a file.");
 fclose (stdout);
 return 0;

}


      </source>