Question

I have the following c program which launches a Gtk Program on ubuntu:

#include <unistd.h>

int main( int argc, const char* argv[] )
{
    char *args[2] = { "testarg", 0 };
    char *envp[1] = { 0 };
    execve("/home/michael/MyGtkApp",args,envp);
}

I get “Gtk-WARNING **: cannot open display: ” and my program is not launched.

I have tried setting char *envp[1] = {"DISPLAY:0.0"}; and execute ‘xhost +‘ , I don’t see the ‘cannot open display’ warning, but my program is still not launched.

Does anyone know how to fix my problem?

Thank you.

Answer 1

char *envp[1] = {"DISPLAY:0.0"};

Very wrong. Separate name and value by =, and terminate the list by NULL like args.

char *envp[2] = {"DISPLAY=:0.0", 0};

or better yet, don’t hard-code the display, and use Xauthority too.

char *display = 0, *xauthority = 0;
char *envp[3] = {0};
asprintf(&display, "DISPLAY=%s", getenv("DISPLAY"));
asprintf(&xauthority, "XAUTHORITY=%s", getenv("XAUTHORITY"));
envp[0] = display;
envp[1] = xauthority;

I’m left wondering why you give the program such a sparse environment, though – depending on how you’re configured and what you’re using, Gtk+ may not be entirely happy with DBUS_SESSION_BUS_ADDRESS,GTK2_RC_FILES,GTK_IM_MODULE,HOME,LANG*,LC_*,PATH,XDG_* etc. environment variables gone. Why don’t you just use execv or execvp, and just allow the parent’s environment to be inherited?