C++ cstring memchr() Function

The C++ cstring memchr() function is used to search the first occurrence of a character in the first n bytes of the memory block that is pointed by the argument str.

Consider a case you need to search name of students, that starts with 'A' in a memory block. In this case, you can use the memchr() function.

If you search for a character that is not present in the memory block, the function will return NULL. If memory block, pointed by ptr does not contain at least n bytes, the results are undefined.

Syntax

We use the following syntax to use the memchr() function −

void *memchr(const void *str, int c, size_t n);

Parameters

Parameters of the memchr() function are as follows −

• str: This is the pointer to the memory block where the search is performed.
• c: This is the character to be located. It is passed as its int promotion.
• n: This is the number of bytes to be analyzed.

Return Value

The memchr() function returns a pointer to the first occurrence of the character c in the memory block, or NULL if the character does not occur in the given memory block.

Example 1

Following example demonstrates the basic usage of the memchr() function.

In this example we will take a memory block str and then search for the first occurrence of the character 'A' in the first 5 bytes of the memory block using the memchr() function.

#include <iostream>
#include <cstring>
using namespace std;

int main() {
   char str[] = "tutorialspoint";
   char *ret;

   ret = (char*)memchr(str, 't', 5);

   if(ret) {
      cout << "Character found: " << *ret << endl;
   } else {
      cout << "Character not found" << endl;
   }

   return 0;
}

Output

Following is the output of the above C++ program:

Character found: a

Example 2

Now, let's take another example where we will search for the character that is not present in the memory block.

For this, we will take a memory block str and then search for the first occurrence of the character 'z' in the first 5 bytes of the memory block using the memchr() function.

#include <iostream>
#include <cstring>
using namespace std;

int main() {
   char str[] = "tutorialspoint";
   char *ret;

   ret = (char*)memchr(str, 'z', 5);

   if(ret) {
      cout << "Character found: " << *ret << endl;
   }else {
      cout << "Character not found" << endl;
   }

   return 0;
}

Output

Following is the output of the above C++ program −

Character not found