// TCPServer.cpp
void TCPServer::acceptConnections(/*...*/const char* (*requestHandler)(char* request)) {
    /*...*/

    char* buffer = new char[readBufferSize];
    buffer = {0};

    /* ...Write request stuff to buffer */

    const char* response = requestHandler(buffer); // segmentation fault happening here

    delete[] buffer;

    /*...*/
}

// main.cpp

#include "TCPServer/TCPServer.hpp"

const char* tcpRequestHandler(char* buffer);

int main() {
    TCPServer server = TCPServer(8080, 1024);

    server.boot();

    // passing pointer to tcpRequestHandler
    server.acceptConnections(1024, &tcpRequestHandler);
}

const char* tcpRequestHandler(char* buffer) {
    return "test";
}