C string.h Library

C Tutorial

C string.h Library

In C string.h Library provides functions to manipulate and handle strings (character arrays). It’s one of the most widely used libraries for string operations.

📌 Common String Functions

1️⃣ String Length and Copy

Function Description
strlen(const char *str) Returns the length of the string (excluding \0)
strcpy(char *dest, const char *src) Copies src string into dest
strncpy(char *dest, const char *src, size_t n) Copies first n characters of src to dest

Example:


 

2️⃣ String Concatenation

Function Description
strcat(char *dest, const char *src) Appends src at the end of dest
strncat(char *dest, const char *src, size_t n) Appends first n characters of src to dest

Example:


 

3️⃣ String Comparison

Function Description
strcmp(const char *str1, const char *str2) Compares two strings, returns 0 if equal
strncmp(const char *str1, const char *str2, size_t n) Compares first n characters
strcasecmp / strncasecmp Case-insensitive comparison (POSIX)

Example:


 

4️⃣ Searching in Strings

Function Description
strchr(const char *str, int c) Returns pointer to first occurrence of c
strrchr(const char *str, int c) Returns pointer to last occurrence of c
strstr(const char *haystack, const char *needle) Returns pointer to first occurrence of needle substring

Example:


 

5️⃣ String Tokenization

Function Description
strtok(char *str, const char *delim) Splits string into tokens based on delimiters

Example:


 

6️⃣ String Transformation

Function Description
toupper(int c) / tolower(int c) Convert character case
memset(void *ptr, int value, size_t num) Fill memory with value
memcpy(void *dest, const void *src, size_t n) Copy memory block
memcmp(const void *ptr1, const void *ptr2, size_t n) Compare memory block

Example:


 

7️⃣ Dynamic String Example


 

📌 Summary Table

Function Purpose
strlen Get string length
strcpy, strncpy Copy strings
strcat, strncat Concatenate strings
strcmp, strncmp Compare strings
strchr, strrchr Find character in string
strstr Find substring
strtok Tokenize string
toupper, tolower Convert character case
memset, memcpy, memcmp Manipulate memory

✅ Notes

  1. Strings in C are arrays of characters ending with \0.

  2. Always ensure enough space in destination arrays for strcpy/strcat.

  3. Prefer strncpy and strncat for safe operations.

  4. Use dynamic memory for strings of unknown length.

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