Bases du traitement des fichiers C

#include <stdio.h>
int main() {
   FILE *fp;
   char *filename = "sample.txt";
   char *content = "Hey there! You&#39;ve successfully created a file with content in c programming language.";
   /* open for writing */
   fp = fopen(filename, "w");
   if( fp == NULL ) {
      printf("%s: failed to open. </p><p>", filename);
      return -1;
   } else {
      printf("%s: opened in write mode.</p><p>", filename);
   }
   /* Write content to file */
   fprintf(fp, "%s</p><p>", content);
   if( !fclose(fp) )
      printf("%s: closed successfully.</p><p>", filename);
   return 0;
}

sample.txt: opened in write mode.
sample.txt: closed successfully.

#include <stdio.h>
int main() {
   FILE *fp;
   char *filename = "file_read.txt";
   char ch;
   /* open for writing */
   fp = fopen(filename, "r");
   if (fp == NULL) {
      printf("%s does not exists </p><p>", filename);
      return;
   } else {
      printf("%s: opened in read mode.</p><p></p><p>", filename);
   }
   while ((ch = fgetc(fp) )!= EOF) {
      printf ("%c", ch);
   }
   if (!fclose(fp))
      printf("</p><p>%s: closed.</p><p>", filename);
   return 0;
}

file_read.txt: opened in read mode.
You have opened a file using C programming language, in read-only mode.
file_read.txt: closed.

This text was already there in the file.

#include <stdio.h>
int main() {
   FILE *fp;
   char ch;
   char *filename = "file_append.txt";
   char *content = "This text is appeneded later to the file, using C programming.";
   /* open for writing */
   fp = fopen(filename, "r");
   printf("</p><p>Contents of %s -</p><p></p><p>", filename);
   while ((ch = fgetc(fp) )!= EOF) {
      printf ("%c", ch);
   }
   fclose(fp);
   fp = fopen(filename, "a");
   /* Write content to file */
   fprintf(fp, "%s</p><p>", content);
   fclose(fp);
   fp = fopen(filename, "r");
   printf("</p><p>Contents of %s -</p><p>", filename);
   while ((ch = fgetc(fp) )!= EOF) {
      printf ("%c", ch);
   }
   fclose(fp);
   return 0;
}

Contents of file_append.txt -
This text was already there in the file.
Appending content to file_append.txt...
Content of file_append.txt after 'append' operation is -
This text was already there in the file.
This text is appeneded later to the file, using C programming.