How to Compare Last n Characters of A String to Another String in C

Question

Imagine that I have two strings, one of them is a url like "/sdcard/test.avi" and the other one is"/sdcard/test.mkv". I want to write an if statement that looks whether the last four characters of string is ".avi" or not in C. How can I do this? Using strcmp or what and how?

Answer 1

If you have a pointer-to-char array, str, then this:

int len = strlen(str);
const char *last_four = &str[len-4];

will give you a pointer to the last four characters of the string. You can then use strcmp(). Note that you'll need to cope with the case where (len < 4), in which case the above won't be valid.

Answer 2

How about this...

if (!strcmp(strrchr(str, '\0') - 4, ".avi")){
    //The String ends with ".avi"
}

char *strrchr(const char *str, int c) - Returns a pointer to the last matching char found in the string, including the NULL char if you so specify. In this case, I use it to get a pointer to the end of the string and then I move the pointer 4 steps back, thus giving a Pointer to the last 4 chars of the string.

I then compare the last 4 chars, to ".avi" and if they match, strcmp returns a 0 or logic FALSE, which I invert in my 'if' condition.