What is Standard Library in C?

What is the Standard Library in C?

The Standard Library in C is a set of pre-written functions and macros that come bundled with your C compiler. These functions help you do common programming tasks like:

• Input and output
• String handling
• Math operations
• Memory management
• File handling
• Time manipulation
• Error handling

Instead of writing your own code for these tasks, you can use functions from the standard library.

Why Use the Standard Library?

Here are some reasons why the C Standard Library is useful:

• Saves Time: No need to write basic code again and again.
• Well-Tested: These functions are reliable and widely used.
• Portable: They work across different systems and compilers.
• Efficient: Most functions are optimized for performance.

Common C Standard Library Header Files and Their Purpose

Examples of Standard Library in C

1. <stdio.h> – Standard Input/Output

It is used for Input and output functions like printf, scanf, fgets, etc.

#include <stdio.h>
 
int main() {
    printf("Hello from Sanfoundry!\n");
    return 0;
}

Output:

Hello from Sanfoundry!

2. <stdlib.h> – Standard Library

It is used for Memory allocation, process control, conversions, etc.

#include <stdlib.h>
#include <stdio.h>
 
int main() {
    int *ptr = (int *)malloc(sizeof(int));
    *ptr = 100;
    printf("Value = %d\n", *ptr);
    free(ptr);
    return 0;
}

Output:

Value = 100

3. <string.h> – String Handling

It is used for Operations like strcpy, strlen, strcmp, etc.

#include <string.h>
#include <stdio.h>
 
int main() {
    char str1[] = "Sanfoundry";
    char str2[20];
    strcpy(str2, str1);
    printf("Copied string: %s\n", str2);
    return 0;
}

Output:

Copied string: Sanfoundry

4. <math.h> – Mathematical Functions

It is used for sqrt, pow, sin, cos, etc.

#include <math.h>
#include <stdio.h>
 
int main() {
    double result = pow(2, 3);  // 2^3 = 8
    printf("2 raised to power 3 is %.0f\n", result);
    return 0;
}

Output:

2 raised to power 3 is 8

5. <ctype.h> – Character Handling

It is used for Check character types like isdigit, isalpha, tolower, etc.

#include <ctype.h>
#include <stdio.h>
 
int main() {
    char c = 'A';
    if (isalpha(c)) {
        printf("%c is an alphabet.\n", c);
    }
    return 0;
}

Output:

A is an alphabet.

6. <time.h> – Date and Time Functions

It is used to getting system time, measuring program execution time, delays, etc.

#include <stdio.h>
#include <time.h>
 
int main() {
    time_t now;
    time(&now);
    printf("Current time: %s", ctime(&now));
    return 0;
}

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