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File handling in C allows you to perform operations like creating, reading, writing, and closing files. The C Standard Library provides several functions to handle files efficiently. Here’s a detailed explanation of some of the most commonly used functions: ‘fopen‘, ‘fclose‘, ‘fread‘, ‘fwrite‘, ‘fprintf‘, and ‘fscanf‘.
1. fopen
The ‘fopen‘ function is used to open a file. It returns a pointer to a ‘FILE‘ object that represents the file. The syntax is:
FILE *fopen(const char *filename, const char *mode);
filename: A string that contains the name of the file to be opened.mode: A string that specifies the file access mode (e.g., read, write, append).
Common modes include:
"r": Open for reading. The file must exist."w": Open for writing. If the file exists, it will be truncated to zero length; if it does not exist, it will be created."a": Open for appending. Writes data at the end of the file. The file is created if it does not exist."r+": Open for both reading and writing. The file must exist."w+": Open for both reading and writing. If the file exists, it will be truncated; if it does not exist, it will be created."a+": Open for both reading and appending. The file is created if it does not exist.
Example:
FILE *fp = fopen("example.txt", "r");
if (fp == NULL) {
perror("Error opening file");
}
2. fclose
The ‘fclose‘ function is used to close a file opened by ‘fopen‘. The syntax is:
int fclose(FILE *stream);
stream: A pointer to theFILEobject that represents the open file.
Returns 0 if successful, or EOF if an error occurs.
Example:
if (fclose(fp) != 0) {
perror("Error closing file");
}
3. fread
The ‘fread‘ function reads data from a file. The syntax is:
size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream);
ptr: Pointer to a buffer where the read data will be stored.size: Size in bytes of each element to be read.nmemb: Number of elements to be read.stream: Pointer to theFILEobject.
Returns the number of elements successfully read.
Example:
char buffer[100];
size_t n = fread(buffer, sizeof(char), 100, fp);
if (n != 100 && ferror(fp)) {
perror("Error reading file");
}
4. fwrite
The ‘fwrite‘ function writes data to a file. The syntax is:
size_t fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream);
ptr: Pointer to the data to be written.size: Size in bytes of each element to be written.nmemb: Number of elements to be written.stream: Pointer to theFILEobject.
Returns the number of elements successfully written.
Example:
const char *data = "Hello, World!";
size_t n = fwrite(data, sizeof(char), strlen(data), fp);
if (n != strlen(data)) {
perror("Error writing file");
}
5. fprintf
The ‘fprintf‘ function writes formatted output to a file. The syntax is:
int fprintf(FILE *stream, const char *format, ...);
stream: Pointer to theFILEobject.format: A string that specifies the format of the output, similar toprintf.
Returns the number of characters written, or a negative value if an error occurs.
Example:
int age = 25;
fprintf(fp, "Age: %d\n", age);
6. fscanf
The ‘fscanf‘ function reads formatted input from a file. The syntax is:
int fscanf(FILE *stream, const char *format, ...);
- ‘
stream‘: Pointer to the ‘FILE‘ object. - ‘
format‘: A string that specifies the format of the input, similar to ‘scanf‘.
Returns the number of input items successfully matched and assigned.
Example:
int age;
fscanf(fp, "%d", &age);
Example Program
Here’s a complete example demonstrating these functions:
#include <stdio.h>
#include <stdlib.h>
int main() {
FILE *fp;
char buffer[100];
// Open a file for writing
fp = fopen("example.txt", "w");
if (fp == NULL) {
perror("Error opening file for writing");
return EXIT_FAILURE;
}
// Write to the file
fprintf(fp, "Hello, World!\n");
fclose(fp);
// Open the file for reading
fp = fopen("example.txt", "r");
if (fp == NULL) {
perror("Error opening file for reading");
return EXIT_FAILURE;
}
// Read from the file
if (fgets(buffer, sizeof(buffer), fp) != NULL) {
printf("Read from file: %s", buffer);
} else {
perror("Error reading from file");
}
fclose(fp);
return EXIT_SUCCESS;
}
This program writes “Hello, World!” to a file and then reads it back, displaying the content on the console.
