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C Programming: Mastering File Handling
Up until now, your programs lose all data the moment they close. To keep data permanently, you must store it on the hard drive. C uses file handling to open, read, write, and close physical files on your system.
The Six Core File Functions
- fopen(): Opens a file and establishes a stream. You choose a mode: read (
"r"), write ("w"), or append ("a"). - fclose(): Closes the open file stream, saving changes and clearing system locks.
- fprintf(): Writes formatted text strings directly into a file.
- fscanf(): Reads data out of a file based on specific format specifiers.
- fgets(): Reads an entire string line safely from a file.
- fputs(): Writes an entire string line smoothly into a file.
Problem 1: Word Counter Algorithm
This program opens a text file, reads it character by character, and counts the words by identifying blank spaces and newline markers.
#include <stdio.h>
int main() {
FILE *fp = fopen("sample.txt", "r");
char ch;
int words = 0, inWord = 0;
if (fp == NULL) {
printf("Could not open file!\n");
return 1;
}
while ((ch = fgetc(fp)) != EOF) {
if (ch == ' ' || ch == '\n' || ch == '\t') {
inWord = 0;
} else if (inWord == 0) {
inWord = 1;
words++;
}
}
fclose(fp);
printf("Total Words: %d\n", words);
return 0;
}
int main() {
FILE *fp = fopen("sample.txt", "r");
char ch;
int words = 0, inWord = 0;
if (fp == NULL) {
printf("Could not open file!\n");
return 1;
}
while ((ch = fgetc(fp)) != EOF) {
if (ch == ' ' || ch == '\n' || ch == '\t') {
inWord = 0;
} else if (inWord == 0) {
inWord = 1;
words++;
}
}
fclose(fp);
printf("Total Words: %d\n", words);
return 0;
}
Problem 2: File Duplicator (Copy File)
We read every byte from a source file and clone it cleanly into a destination file block.
#include <stdio.h>
int main() {
FILE *src = fopen("source.txt", "r");
FILE *dest = fopen("destination.txt", "w");
char ch;
if (src == NULL || dest == NULL) {
printf("File access error!\n");
return 1;
}
while ((ch = fgetc(src)) != EOF) {
fputc(ch, dest);
}
fclose(src);
fclose(dest);
return 0;
}
int main() {
FILE *src = fopen("source.txt", "r");
FILE *dest = fopen("destination.txt", "w");
char ch;
if (src == NULL || dest == NULL) {
printf("File access error!\n");
return 1;
}
while ((ch = fgetc(src)) != EOF) {
fputc(ch, dest);
}
fclose(src);
fclose(dest);
return 0;
}
Problem 3: Persistent Student Database Manager
This system saves structural records safely onto the hard drive and reads them back out cleanly.
#include <stdio.h>
struct Student {
int id;
char name[20];
};
int main() {
FILE *fp = fopen("students.dat", "w+");
struct Student s1 = {101, "Raj"};
struct Student s2;
// Write structure data safely into our file stream
fprintf(fp, "%d %s\n", s1.id, s1.name);
// Rewind the file position back to index zero
rewind(fp);
// Read the structure file back out into our empty memory folder
fscanf(fp, "%d %s", &s2.id, s2.name);
printf("Loaded Record: ID: %d, Name: %s\n", s2.id, s2.name);
fclose(fp);
return 0;
}
struct Student {
int id;
char name[20];
};
int main() {
FILE *fp = fopen("students.dat", "w+");
struct Student s1 = {101, "Raj"};
struct Student s2;
// Write structure data safely into our file stream
fprintf(fp, "%d %s\n", s1.id, s1.name);
// Rewind the file position back to index zero
rewind(fp);
// Read the structure file back out into our empty memory folder
fscanf(fp, "%d %s", &s2.id, s2.name);
printf("Loaded Record: ID: %d, Name: %s\n", s2.id, s2.name);
fclose(fp);
return 0;
}
Summary
File handling transfers dynamic data out of volatile RAM and locks it permanently into hard drive storage streams using the robust FILE * controller type.
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