In this article, you will understand different string handling functions in C. By the end of this article, you will learn how to write C programs to perform the following string operations –  find the length of a string, compare 2 strings, copy one string to another, concatenate 2 strings, etc.

Following are some of the useful string handling functions in C.

1. strlen()
2. strcpy()
3. strncpy()
4. strcat()
5. strncat()
6. strcmp()
7. strncmp()
8. strcmpi()
9. strncmpi()

These string handling functions are defined in string.h header file. Hence you need to include this header file whenever you use these string handling functions in your C program.

Following are the most commonly used string handling functions in C. All these functions take either character pointer or character arrays as arguments.

1. 1. strlen()
      strlen() is used to find the length of a string. strlen() function returns the length of a string. It returns an integer value.
      Example:

      char *str = "Learn C Online";
      int strLength;
      strLength = strlen(str);    //strLength contains the length of the string i.e. 14
      

      In the above example, I have declared a string named str and assigned a value – “Learn C Online” to it. In the next line, I have declared an int variable named strLength which will be used to store the length of the string named str. The next line uses the in-built function strlen() which accepts one parameter i.e., a string named str.
      strlen() function will return the length (int type) of the string which be stored in the variable strLength.
      After execution of this line, variable strLength should hold integer value 14.

      Here is the program that demonstrates usage of strlen() string function – visit Find string length using in-built C string function

   2. strcpy()
      strcpy() function is used to copy one string to another. strcpy() function accepts 2 parameters. The first parameter is the destination string i.e. the string variable used to copy the string into. The second parameter is the source string i.e. the string variable or string value that needs to be copied to the destination string variable.

      The Destination_String should be a variable and Source_String can either be a string constant or a variable.

      Syntax:
      strcpy(Destination_String,Source_String);

      Example:

      char *Destination_String;
      char *Source_String = "C String functions";
      strcpy(Destination_String,Source_String);
      printf("%s", Destination_String);
      

      Output:
      C String functions

      In the above example, I have declared 2 strings. The first string variable is named “Destination_String” and the second string is named “Source_String” with a string value assigned to it.
      In the next line, I am using strcpy() function with 2 parameters. This in-built string function will copy the value of Source_String into Destination_String. The variable Destination_String will now hold the value – “C String functions”.

   3. strncpy()
      strncpy() is used to copy only the left-most n characters from source to destination. The Destination_String should be a variable and Source_String can either be a string constant or a variable.
      Syntax:
      strncpy(Destination_String, Source_String,no_of_characters);
   4. strcat()
      strcat() is used to concatenate two strings.
      The Destination_String should be a variable and Source_String can either be a string constant or a variable.
      Syntax:
      strcat(Destination_String, Source_String);
      Example:

      char *Destination_String ="Learn ";
      char *Source_String = "String functions";
      strcat(Destination_String, Source_String);
      puts( Destination_String);

      Output:
      Learn String functions

   5. strncat()
      strncat() is used to concatenate only the leftmost n characters from the source with the destination string.
      The Destination_String should be a variable and Source_String can either be a string constant or a variable.
      Syntax:
      strncat(Destination_String, Source_String,no_of_characters);
      Example:

      char *Destination_String="Visit ";
      char *Source_String = "Learn C Online is a great site";
      strncat(Destination_String, Source_String,14);
      puts( Destination_String);

      Output:
      Visit Learn C Online

1. strcmp()
   strcmp() function is used two compare two strings. strcmp() function does a case-sensitive comparison between two strings. The Destination_String and Source_String can either be a string constant or a variable.
   Syntax:
   int strcmp(string1, string2);
   This function returns an integer value after comparison.
   The value returned is 0 if two strings are equal.
   If the first string is alphabetically greater than the second string then, it returns a positive value.
   If the first string is alphabetically less than the second string then, it returns a negative value
   Example:

   char *string1 = "C Programming";
   char *string2 = "C Programming";
   int ret;
   ret=strcmp(string1, string2);
   printf("%d",ret);
   

   Output:
   0

2. strncmp()
   strncmp() is used to compare only left most ‘n’ characters from the strings.
   Syntax:
   int strncmp(string1, string2,no_of_chars);
   This function returns an integer value after comparison.
   The value returned is 0 if left most ‘n’ characters of two strings are equal.
   If the left-most ‘n’ characters of the first string are alphabetically greater than the left-most ‘n’ characters of second-string then, it returns a positive value.
   If the left-most ‘n’ characters of the first string are alphabetically less than the left-most ‘n’ characters of second-string then, it returns a negative value
   Example:

   char *string1 = "Learn C Online is a great site";
   char *string2 = "Learn C Online";
   int ret;
   ret=strncmp(string1, string2,7);
   printf("%d",ret);
   

   Output:
   0

3. strcmpi()
   strcmpi() function is used two compare two strings. strcmp() function does a case insensitive comparison between two strings. The Destination_String and Source_String can either be a string constant or a variable.
   Syntax:
   int strcmpi(string1, string2);
   This function returns an integer value after comparison.
   Example:

   char *string1 = “Learn C Online”;
   char *string2 = “LEARN C ONLINE”;
   int ret;
   ret=strcmpi(string1, string2);
   printf("%d",ret);

   Output:
   0

4. strncmpi()
   strncmpi() is used to compare only left most ‘n’ characters from the strings. strncmpi() function does a case insensitive comparison.
   Syntax:
   int strncmpi(string1, string2,no_of_chars);
   This function returns an integer value after comparison.
   Example:

   char *string1 = "Learn C Online is a great site";
   char *string2 = "LEARN C ONLINE";
   int ret;
   ret=strncmpi(string1, string2,7);
   printf("%d",ret);
   

   Output:
   0