gtk_init changes sprintf functionality

Question

I'm starting to work with Linux and GTK and ran in a strange problem. I am using sprintf() in my code to parse a float into a char array.

When parsing the number 1 into the string this resulted in "1.000000" but strangely after calling gtk_init() when I then do the sprintf it results in "1,000000". How does gtk_init() modify this behavior and how can I force the program to keep parsing it to "1.000000".

This is my small example program that reproduces the problem:

#include <gtk/gtk.h>

int main(int argc, char** argv)
{
    char cMessage[12];
    float fNumber = 1;
    sprintf(cMessage, "T:%f", fNumber);
    printf("%s\n", cMessage);

    gtk_init(&argc, &argv);

    sprintf(cMessage, "T:%f", fNumber);
    printf("%s\n", cMessage);

    return 0;
}

The output of this program is the following:

T:1.000000
T:1,000000

Seems like a locale issue. Does it help if you put setlocale(LC_ALL, "en_US.UTF-8"); as the first line in main? — Blaze
– Blaze, Commented Oct 1, 2018 at 12:57
Not your problem, but: char cMessage[12] in this code is an accident waiting to happen. You've got very little leeway in that buffer if the formatted string ends up slightly longer than you expect. I'd suggest (a) char cMessage[30], and/or (better) snprintf(cMessage, sizeof(cMessage), "T:%f", fNumber);. — Steve Summit
– Steve Summit, Commented Oct 1, 2018 at 14:13

wazoox · Accepted Answer · 2018-10-01 12:59:38Z

7

This is related to your locale/language environment. Before calling gtk_init, you LOCALE variable must be set the the default value, C. gtk_init by default, sets the locale to whatever your desktop environment is set to.

To turn this behaviour off, you can use gtk_disable_setlocale.

answered Oct 1, 2018 at 12:59

wazoox

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