How to override c++ string class with LD_PRELOAD

Question

i am trying to override predefined functions such as strcmp, getenv, etc. i already override some of them using LD_PRELOAD options. but i can't override string class, how can i override c++ string class

i already tried something like this;

class string{
    char* str;
public:
    string (char* str2){
        str = str2;
        std::cout << str2 << std::endl ;
    }
    bool operator==(char* str2)  {
        std::cout << "c++ => " << str << "==" << str2 << std::endl;
        return false; 
    }
    compare(char* str2)  {
        std::cout << "c++ => " << str << "==" << str2 << std::endl;
        return 0;
    }
};  

but it doesn't work i can't print the string that compared or even defined.

compile;

g++ -g -Wall -shared -fPIC -ldl -o bypasscpp.so bypass.cpp

And running program with;

LD_PRELOAD="./bypasscpp.so" ./app

Answer 1

Are you trying to override std::string? Please check https://en.cppreference.com/w/cpp/string/basic_string. std::string is just a typedef for std::basic_string<char> which means that std::string is not dynamically linked. In other words those methods you try to override are statically linked into you ./app.