Demo of strrchr C function

basename.c

// https://en.cppreference.com/w/c/string/byte/strrchr

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

int main(int argc, char* argv[])
{
    if(argc < 2)
        return -1;

    const char pathsep = '/';
    const char* path = argv[1];

    const char* slash = strrchr(path, pathsep);
    const char* basename = slash ? (slash + 1) : path;
    puts(basename);
    return 0;
}

dirname.c

// https://en.cppreference.com/w/c/string/byte/strrchr

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

int main(int argc, char* argv[])
{
    if(argc < 2)
        return -1;

    const char pathsep = '/';
    char* path = argv[1];
    
    size_t path_len = strlen(path);
    if(path_len > 0 && path[path_len - 1] == pathsep)
        path[path_len - 1] = '\0';

    const char* slash = strrchr(path, pathsep);
    size_t dirname_len = slash != NULL ? (slash - path) : 0;

    if(slash != NULL && dirname_len > 0)
    {
        path[dirname_len] = '\0';
        puts(path);
    }
    else if(slash != NULL && dirname_len == 0)
    {
        path[dirname_len + 1] = '\0';
        puts(path);
    }
    else
    {
        puts(".");
    }

    return 0;
}