Question

I’m noob in C++ but wanting to learn. I have a little program that writes some info to my \etc\hosts in Windows; I get the %WINDIR% variable via GetEnvironmentVariable(), if I put the full path manually everything is ok, but when I substitute with WINDIR variable my code isn’t compiling. I know I don’t do something right.

#include <windows.h>
#include <ios>
#include <fstream>

char buffer[1000];
int main() {
    GetEnvironmentVariable("WINDIR",(char*)&buffer,sizeof(buffer));
    std::ofstream log;
    log.open("%s\\system32\\drivers\\etc\\hosts", buffer);
    log << "127.0.0.1   domain.com\n" << std::endl;
    return 0;
}

I get really ugly errors like:

C:\Documents and Settings\xtmtrx\Desktop\coding\windir.cpp no matching function for call to `std::basic_ofstream<char, std::char_traits<char> >::open(const char[30], char[1000])‘

Answer 1

ofstream cannot format the path for you. You need to do that separately, eg:

#include <windows.h>
#include <ios>
#include <fstream>

char buffer[1000] = {0};
int main() {
    GetEnvironmentVariable("WINDIR",buffer,sizeof(buffer));
    strcat(buffer, "\\system32\\drivers\\etc\\hosts");
    std::ofstream log;
    log.open(buffer, ios_base::ate);
    log << "127.0.0.1   domain.com\n" << std::endl;
    return 0;
}

FYI, you should use GetWindowsDirectory(), GetSystemDirectory(), SHGetSpecialFolderPath() or SHGetKnownFolderPath() instead of GetEnvironmentVariable(). And you should use PathCombine() when concantenating paths together so it can ensure the slashes are correct.