How to Use the Strncmp Function in C++

The C++ strncmp function compares a specified number of bytes between two strings. It returns 0 if they are equal to each other and a nonzero value to indicate which string is greater. The following steps will help you use the function strncmp in C++.

Instructions

1. Learn the syntax of strncmp in C++. The complete syntax is int strncmp (const char *pointer1, const char *pointer2, size_t num);.

2. Notice that pointer1 and pointer2 are pointers to characters. strncmp starts at the beginning of each string and begins comparing characters until they differ or a null terminating character is read or num bytes have been compared. Strncmp returns a zero if all bytes match. Strncmp returns a positive integer if the first non-matching byte as an unsigned char is greater for pointer1; otherwise it returns a negative integer.

3. Understand that the C++ strncmp function is kept in the cstring library. You may need to include the string.h header file to use this function.

4. #include
   #include

   int main ()
   {
   char string1[][3] = { "archer" , "arrange" , "array" };
   int n;
   puts ("Looking for words beginning with arr...");
   for (n=0 ; n<3 ; n++)
   if (strncmp (string1[n],"arr",3) == 0)
   printf ("found %s\n",string1[n]);
   return 0;
   }

   Observe the following output for this program:

   Looking for words beginning with arr...
   found arrange
   found array

5. Observe the following output for this program:

   Looking for words beginning with arr...
   found arrange
   found array

   Notice that strncmp did not match "archer" with "arr" because we are comparing the first three characters.

Resources

• Learn more about using strncmp in C++.