C String Functions

What You’ll Find Here

The C standard library provides dozens of string and memory functions in <string.h> for copying text, comparing names, searching substrings, tokenizing CSV lines, and handling locale-aware sorting. This page is your central hub: browse every function in our tutorial series, jump to full guides with examples and output, and learn patterns that work in real C programs.

Introduction

In C, strings are null-terminated arrays of char. You work with them through library functions such as strlen(), strcpy(), strcmp(), and strstr()—not methods on an object like C# or Java. Most live in <string.h>; locale helpers like strcoll() and strxfrm() also need <locale.h>.

C strings are low-level: you manage buffer sizes, null terminators, and whether a function reads or writes memory. Understanding that distinction prevents buffer overflows and undefined behavior.

🚀 Usage Tips

• Size your buffers — before strcpy or strcat, ensure the destination has room for existing text plus new bytes plus '\0'.
• Prefer bounded copies — use strncpy and strncat when lengths are known; always null-terminate if the copy may fill the buffer.
• Search smartly — strchr for one character, strstr for substrings, strspn/strcspn for parsing without destroying the string.
• Tokenize carefully — strtok modifies the buffer and is not thread-safe; copy first or use strtok_r on POSIX.
• Know extensions — strlwr, strupr, strrev, and strdup are not ISO C; tutorials include portable alternatives.
• Read the tutorial — each linked function page includes syntax, five examples, a quick reference table, and FAQs.

📝 How to Call a String Function

Every C string function follows the same general pattern:

#include <string.h>
return_type function_name(char *dest, const char *src, ...);

Common Patterns

Functions vs Methods (C vs C#)

C has no String class. You call free functions with pointers. If you also learn C#, compare this page with our C# String Methods index—there you use dot notation (text.Contains("x")) on immutable string objects.

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

int main(void) {
    char line[] = "  Hello, C!  ";
    char *token;
    size_t len = strlen(line);

    printf("Length: %zu\n", len);

    token = strtok(line, " ");
    while (token != NULL) {
        printf("Token: %s\n", token);
        token = strtok(NULL, " ");
    }

    return 0;
}