File IO operations in C.

file-io.c

// file-io.h
//
// #ifndef FILE_IO_H
// #define FILE_IO_H
//
// // Read and write files.
// // filename      - The file's name.
// // buffer        - Buffer that will contain file characters.
// // buffer_length - The length of the buffer.
// //
// // Returns 1 if any error has occurred.
// char fio_read(const char* filename, char* buffer, unsigned long int* buffer_length);
// char fio_write(const char* filename, char* buffer, unsigned long int* buffer_length);
//
// #endif

// If file-io.h is present, you may uncomment this line.
// #include "file-io.h"

// Include FILE operations and IO functions
#include <stdio.h>
#include <stdlib.h>

// Read a file.
// filename         - Name of file.
// buffer           - Buffer that will contain file output.
// buffer_length    - Length of the buffer.
//
// Returns a value of 1 if an error occurred, otherwise returns 0.
char fio_read(const char* filename, char* buffer, unsigned long int* buffer_length) {
  // Open the file for reading.
  FILE* file = fopen(filename, "r");
  
  // If the file could not be opened, print an error and return 1.
  if (file == NULL) {
    fprintf(stderr, "Error: Can't read file %s.\n", filename);
    fclose(file);
    file = NULL;
    return 1;
  }
  
  // Get the file's length and store it in buffer_length.
  fseek(file, 0L, SEEK_END);      // Go to the end of the file.
  *buffer_length = ftell(file);   // Store the file's length.
  fseek(file, 0L, SEEK_SET);      // Go to the start of the file.
  
  // Loop over file's characters one-by-one and store them in the buffer.
  for (unsigned long int i = 0; i < *buffer_length; ++i) {
    *(buffer + i) = (char) fgetc(file);
  }
  
  // No errors occurred.
  return 0;
}

// Write a file.
// filename       - The file's name.
// buffer         - The input buffer.
// buffer_length  - The length of the input buffer.
//
// Returns 1 if error.
char fio_write(const char* filename, char* buffer, unsigned long int* buffer_length) {
  // Open the file for writing.
  FILE* file = fopen(filename, "w");
  
  // If the file couldn't be opened, print an error and return 1.
  if (file == NULL) {
    fprintf(stderr, "Error: Couldn't write file %s.\n", filename);
    fclose(file);
    file = NULL;
    return 1;
  }
  
  // Write to the file character-by-character.
  for (unsigned long int i = 0; i < *buffer_length; ++i) {
    fputc(file, *(buffer + i));
  }
  
  // No errors occurred.
  return 0;
}