<string.h> header functions (3) - Comparison

Compare Functions

strcmp : Compare two strings

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

str1 : C string to be compared

str2 : C string to be compared

Return Value

• <0 : The first character that does not match has a lower value in ptr1 than in ptr2
• 0 : The contents of both strings are equal
• >0 : The first character that does not match has a greater value in ptr1 than in ptr2

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

int main ()
{
  char key[] = "apple";
  char buffer[80];
  do {
     printf ("Guess my favorite fruit? ");
     fflush (stdout);
     scanf ("%79s",buffer);
  } while (strcmp (key,buffer) != 0);
  puts ("Correct answer!");
  return 0;
}

Guess my favorite fruit? apple
Guess my favorite fruit? orange
Correct answer!

---

strncmp : Compare characters of two strings

int strncmp(const char* str1, const char* str2, size_t num);

str1 : C string to be compared

str2 : C string to be compared

num : Maximum number of characters to compare

Return Value

• <0 : The first character that does not match has a lower value in str1 than in str2
• 0 : The contents of both strings are equal
• >0 : The first character that does not match has a greater value in str1 than in str2

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

int main ()
{
  char str[][5] = { "R2D2" , "C3PO" , "R2A6" };
  int n;
  puts ("Looking for R2 astromech droids...");
  for (n=0 ; n<3 ; n++)
    if (strncmp (str[n],"R2xx",2) == 0)
    {
      printf ("found %s\n",str[n]);
    }
  return 0;
}

Looking for R2 astromech droids...
found R2D2
found R2A6

---

strcoll : Compare two strings using locale

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

str1 : C string to be compared

str2 : C string to be compared

Return Value

• <0 : The first character that does not match has a lower value in str1 than in str2
• 0 : The contents of both strings are equal
• >0 : The first character that does not match has a greater value in str1 than in str2

Not Using this Function Usually

---

strxfrm : Transform string using locale

size_t strxfrm(char* destination, const char* source, size_t num);

destination : Pointer to the destination array where the content is to be copieed. (It can be NULL pointer if the argument for num is zero)

source : C string to be transformed

num : Maximum number of characters to be copied to destination

Return Value

The length of the transformed string, not including the terminating null-character.

Not Using this Function Usually