#include <iostream>

using namespace std;

class MyCGI {

    private:
        string env[22];

    public:
        MyCGI();
        ~MyCGI();

};

MyCGI::MyCGI() {

    char *envName[22] = {
        "AUTH_TYPE", "CONTENT_LENGTH", "CONTENT_TYPE",
        "GATEWAY_INTERFACE", "HTTP_ACCEPT", "HTTP_CONNECTION",
        "HTTP_HOST", "HTTP_REFERER", "HTTP_USER_AGENT",
        "PATH_INFO", "PATH_TRANSLATET", "QUERY_STRING",
        "REMOTE_ADDR", "REMOTE_HOST", "REMOTE_IDENT",
        "REMOTE_USER", "REQUEST_METHOD", "SCRIPT_NAME",
        "SERVER_NAME", "SERVER_PORT", "SERVER_PROTOCOL",
        "SERVER_SOFTWARE"
    };

    for(int i = 0; i < sizeof(envName) / sizeof(*envName); i++) {
        env[i] = getenv(envName[i]); // Bumm!!!!!!!!!!!!!!!!!!!!!!!!!!
        cout << env[i] << '\n';
    }

    cout << "Env-Beispiel: " << env[3] << '\n';
}

MyCGI::~MyCGI() {
}

int main(int argc, char *argv[]) {
    cout << "Content-Type: text/html\n\n";
    MyCGI CGIInst;
    return 0;
}

Return Value
A null-terminated string with the value of the requested environment variable, or NULL if that environment variable does not exist.

Also machst du dann:

char const* p = 0;
std::string str(p);

Garantiertes undefiniertes Verhalten

Du musst einfach zuerst den Fehlerfall abfangen.

Grüssli