How to get file extension from string in C++

Question

Given a string \"filename.conf\", how to I verify the extension part?

I need a cross platform solution.

Answer 1

For char array-type strings you can use this:

#include 
#include 

int main()
{
    char filename[] = "apples.bmp";
    char extension[] = ".jpeg";

    if(compare_extension(filename, extension) == true)
    {
        // .....
    } else {
        // .....
    }

    return 0;
}

bool compare_extension(char *filename, char *extension)
{
    /* Sanity checks */

    if(filename == NULL || extension == NULL)
        return false;

    if(strlen(filename) == 0 || strlen(extension) == 0)
        return false;

    if(strchr(filename, '.') == NULL || strchr(extension, '.') == NULL)
        return false;

    /* Iterate backwards through respective strings and compare each char one at a time */

    for(int i = 0; i < strlen(filename); i++)
    {
        if(tolower(filename[strlen(filename) - i - 1]) == tolower(extension[strlen(extension) - i - 1]))
        {
            if(i == strlen(extension) - 1)
                return true;
        } else
            break;
    }

    return false;
}

Can handle file paths in addition to filenames. Works with both C and C++. And cross-platform.