String Functions

Introduction

String functions from string.h — strlen, strcpy, strcat, strcmp, and safer variants strncpy, strncat.

Understanding the topic

strlen Returns length excluding null terminator.

strcpy / strncpy Copy string — strncpy limits bytes copied.

strcmp Compare lexicographically — 0 if equal.

• strlen — Returns length excluding null terminator.
• strcpy / strncpy — Copy string — strncpy limits bytes copied.
• strcmp — Compare lexicographically — 0 if equal.

Step-by-step explanation

1. strlen — Returns length excluding null terminator.
2. strcpy / strncpy — Copy string — strncpy limits bytes copied.
3. strcmp — Compare lexicographically — 0 if equal.

Syntax reference

Syntax reference:

#include <string.h>

Informative example

Example program:

#include <stdio.h>
#include <string.h>

int main(void) {
    char a[20] = "Hello";
    strcat(a, " C");
    printf("%s len=%zu\n", a, strlen(a));
    return 0;
}

Hello C len=7

Execution workflow

Best practices

• Enable warnings: gcc -Wall -Wextra -std=c11 source.c -o app
• Give every variable a defined value before it is read.
• Stay inside array bounds — C will not stop you from over-running a buffer.

Common mistakes

• strcpy buffer overflow if destination too small

Hands-on exercise

Practice problems:

• Compare two strings
• Copy with strncpy safely

Summary

String Functions in C — Common helpers from string.