CODEWITHSUNDEEP
c++string
user3260595
user3260595

Reputation: 53

fastest way to compare unsigned char* and const char*

What is the fastest way to compare unsigned char* and const char* ?

Say, I have

    unsigned char* msg;  //length is more than 10000
    typedef struct {
      atomic<bool> updated;
      const char cmp[10]="test    ";
      int id=10000;
    } test;

I want to compare msg ( starting from 30th characters) to test.cmp upto 5 length. I am doing the following code

    for (int k = 0; k < 5; k++) {
            if (*(msg + 30+ k) != test.cmp[k]) {
                break;
            }

    }

Is the correct way or do you suggest something else?

Thanks a lot.

Upvotes: 2

Views: 6507

Answers (2)

naab
naab

Reputation: 1140

use strncmp, this way you can compare the first 5 characters, and by passing msg+30, the first character is the 30th

if (strncmp(reinterpret_cast<const char*>(msg+30), &(test.cmp), 5)==0){
    printf("match");
}

http://www.cplusplus.com/reference/cstring/strncmp/

Using memcmp is a mistake, because cmp is a NULL terminated string and memcmp won't terminate the comparison on the NULL byte.

Upvotes: 4

CucumisSativus
CucumisSativus

Reputation: 320

You can give memcmp try. Although i don't know if it will work properly while comparing pointers which differ in sings.

You can also try to change type of msg to just char *, if it does not collide with the rest of your program and use strcmp or strncmp

Upvotes: 0

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