C Exercises: File read and write using variable

Last update on August 08 2025 12:52:57 (UTC/GMT +8 hours)

17. File Read/Write Variable

Write a program in C to read from a file into a variable and write a variable's contents into a file.

Sample Solution:

C Code:

#include <stdio.h>

int main(int argc, char **argv) {
  FILE *in, *out;
  int c, str;
   
  in = fopen("i.txt", "r");
  if (!in) {
    fprintf(stderr, "Error opening i.txt for reading.\n");
    return 1;
  }
  out = fopen("o.txt", "w");
  if (!out) {
    fprintf(stderr, "Error opening output.txt for writing.\n");
    fclose(in);
    return 1;
  }
  while ((c = fgetc(in)) != EOF) {
    fputc(c, out);
  }
  fclose(out);
  fclose(in);
  return 0;
}

Sample Output:

Error opening i.txt for reading.

Flowchart:

For more Practice: Solve these Related Problems:

Write a C program to read a configuration value from a file and update it dynamically, then write back to the file.
Write a C program to read a file into a variable, modify the content, and write the modified content to a new file.
Write a C program to load file content into a variable, perform a search-and-replace operation, and save the result.
Write a C program to read a file's content into a dynamically allocated string, process the string, and write it back.

Go to:

PREV : Common Directory Tree.
NEXT : Display Last Modification Time.

C Programming Code Editor:

Have another way to solve this solution? Contribute your code (and comments) through Disqus.