std::rename

#include <cstdio>
#include <iostream>
                                                                                                                
using std::rename,
    std::perror,
    std::FILE,
    std::fopen,
    std::fclose,
    std::cerr;

int main(){
    auto fileRename = [](FILE* f){
        if(f == nullptr){
            const char ch[100]{"The result\0"};
            perror(ch);
        }else{
            cerr << "File exists. Rename it.\n";
            rename("ztext.txt", "ztextII.txt");
        }
    };

    FILE* f = fopen("ztext.txt", "a+");//if the file doesn't exist a+ tells it to create it.
    fileRename(f);
    if(f != nullptr){
        fclose(f);
    }
    return 0;
}