C String Functions with Examples

One of the most frequently used data types in all computer languages is the string. Strings are described in C as arrays of characters that end in the null character “0.” Writing C programs that store, manipulate, or communicate textual data requires proper string handling.

Explanation of Strings in C

Strings are kept in C as arrays of the char data type. A string’s characters each take up one byte of memory. The string’s final character is always the null terminator ‘0’ to indicate the string’s end. For instance:

char str[6] = {'H','e','l','l','o','\0'};

Here, str is an array of 6 characters, including the null terminator. The length of this string is 5 (excluding null).

We can also declare strings like this:

char str[6] = "Hello";

The compiler automatically appends the ‘\0’ at the end.

Strings in C can be initialized but cannot be assigned. For example:

str = "World"; // Error

This is because arrays cannot be assigned in C. We need to use string functions like strcpy() for assignments.

Importance of String Handling in C

• Textual data is very common in applications – names, addresses, messages, etc. Proper string handling helps manage this data efficiently.
• Strings are used for file I/O, network communication, user interaction, data processing, etc., in C. Robust string functions help implement the core functionality.
• Strings in C are stored in simple character arrays. String functions in C are needed for manipulation like concatenation, substring search, case change, etc.
• Safety and security of string operations are also important to avoid bugs like buffer overflows. Secure string functions prevent vulnerabilities.
• Efficiency in string operations affects overall program performance. Optimized string functions improve speed for string-intensive applications.

Basic String Functions in C

C provides a wide range of built-in functions for manipulating strings. Here are some commonly used basic string functions.

strlen() – Finding String Length

Syntax

size_t strlen(const char *str);

Purpose and Description

• strlen() calculates the length of the given null-terminated string str.
• It returns the number of characters in the string excluding the null terminator ‘\0’.
• This function is defined in string.h header file.

Example

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

int main() {
  char str[50] = "Hello, World!";

  int len = strlen(str);

  printf("Length of the string is: %d", len);
  
  return 0;
}

strcpy() – Copying Strings

Syntax

char *strcpy(char *destination, const char *source);

Purpose and Description

• Using the strcpy() function, you can copy a string from the source to the destination character array.
• It returns the destination string.
• Both strings should have enough space to store the content.

Example

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

int main() {
  
  char source[20] = "Hello";
  char destination[20];

  // Copies source to destination
  strcpy(destination, source);

  printf("Destination string: %s", destination);

  return 0;
}

strcat() – Concatenating Strings

Syntax

char *strcat(char *destination, const char *source);

Purpose and Description

• You can copy a string from the source to the target character array using the strcpy() function.
• To save the combined text after concatenation, the destination string must have enough room.
• It returns the destination string.

Example

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

int main() {

  char destination[30] = "Hello";
  char source[15] = "World";

  // Concatenates source to destination
  strcat(destination, source);

  printf("Destination string: %s", destination);

  return 0;
}

strcmp() – Comparing Strings

Syntax

int strcmp(const char *str1, const char *str2);

Purpose and Description

• strcmp() compares two null-terminated strings lexicographically.
• If both strings are equal, it returns 0.
• Returns a negative number if str1 is less than str2.
• Returns a positive number if str1 is greater than str2.

Example

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

int main() {

  char str1[15];
  char str2[15];
  
  strcpy(str1, "Apple");
  strcpy(str2, "Mango");

  int result = strcmp(str1, str2);
  
  if(result == 0) {
    printf("Strings are equal");
  } else if(result > 0) {
    printf("str1 is greater than str2"); 
  } else {
    printf("str1 is less than str2");
  }
  
  return 0;
}

Additional String Functions in C

Here are some more useful string functions provided in C.

strchr() – Finding a Character in a String

Syntax

char *strchr(const char *str, int character);

Purpose and Description

• strchr() searches for the first occurrence of the given character in the string.
• It returns a pointer to the matched character in the string.
• If the character is not found, it returns NULL.

Example

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

int main() {

  char str[50] = "Hello, World!";
  char *result;

  result = strchr(str, 'W');
  
  if(result) {
    printf("Character found at %ld", result-str);
  } else {
    printf("Character not found");
  }

  return 0;
}

strstr() – Finding a Substring in a String

Syntax

char *strstr(const char *str, const char *substr);

Purpose and Description

• strstr() searches for the first occurrence of substring substr in the string str.
• It returns a pointer to the beginning of the substring if found.
• If substr is not found, it returns NULL.

Example

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

int main() {

  char str[100] = "Hello, World!";
  char *result;
  
  result = strstr(str, "World");
  
  if(result) {
    printf("Substring found at %ld", result-str); 
  } else {
    printf("Substring not found");
  }
  
  return 0;
}

char *strtok(char *str, const char *delimiter);

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

int main() {

  char str[100] = "Hello, This is a test";
  char *token;

  // First call
  token = strtok(str, " "); 
  while(token != NULL) {
    printf("%s\n", token);
    
    // Subsequent calls
    token = strtok(NULL, " "); 
  }
  
  return 0;
}

#include <stdio.h>

int main() {

  char str[] = "Hello, World!";
  
  puts(str);
  
  return 0;
}

#include <stdio.h>

int main() {

  char str[100];

  printf("Enter a string: ");
  gets(str);

  printf("You entered: %s", str);
  
  return 0;
}

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

int main() {

  char str[20] = "Hello WORLD"; 
  strlwr(str);
  
  printf("Lowercase string: %s", str);

  return 0;
}

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

int main() {

  char str[20] = "Hello world";
  strupr(str);

  printf("Uppercase string: %s", str);

  return 0;  
}

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

int main() {

  char str[50] = "Hello, World!";

  strrev(str);
  
  printf("Reversed string: %s", str);

  return 0;
}