In GDB on MinGW, how do I make Ctrl-C stop the program?

Question

I'm on Windows, running GDB on an executable built under MinGW. The program has an infinite loop. I want to find it by hitting Ctrl + C. When I do, both the program and GDB exit. All the help on this subject seems to assume I'm on Linux.

kcwu kcwu · Accepted Answer · 2011-03-12T18:17:41

This is because GDB doesn't handle the Ctrl + C event of the GUI (non-console) program properly.

You can find the workaround in Workaround for GDB Ctrl-C Interrupt.

Update: Given that the mingw.org domain expired, here's the code rescued from the Web Archive:

If you find yourself trying to interrupt a program being debugged by GDB with Ctrl-C and failing then this little program will allow you to issue the break from another session. Just run it passing the Windows pid of the process being debugged and GDB will regain control. [To compile, use gcc -o debugbreak -mno-cygwin -mthreads debugbreak.c ]

/* BEGIN debugbreak.c */

#ifndef _WIN32_WINNT
#define _WIN32_WINNT 0x0501
#endif

#if _WIN32_WINNT < 0x0501
#error Must target Windows NT 5.0.1 or later for DebugBreakProcess
#endif

#include <Windows.h>
#include <stddef.h>
#include <stdlib.h>

/* Compile with this line:

    gcc -o debugbreak -mno-cygwin -mthreads debugbreak.c

*/

static char errbuffer[256];

static const char *geterrstr(DWORD errcode)
{
    size_t skip = 0;
    DWORD chars;
    chars = FormatMessage(
        FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
        NULL, errcode, 0, errbuffer, sizeof(errbuffer)-1, 0);
    errbuffer[sizeof(errbuffer)-1] = 0;
    if (chars) {
        while (errbuffer[chars-1] == '\r' || errbuffer[chars-1] == '\n') {
            errbuffer[--chars] = 0;
        }
    }
    if (chars && errbuffer[chars-1] == '.') errbuffer[--chars] = 0;
    if (chars >= 2 && errbuffer[0] == '%' && errbuffer[1] >= '0'
        && errbuffer[1] <= '9')
    {
        skip = 2;
        while (chars > skip && errbuffer[skip] == ' ') ++skip;
        if (chars >= skip+2 && errbuffer[skip] == 'i'
            && errbuffer[skip+1] == 's')
        {
            skip += 2;
            while (chars > skip && errbuffer[skip] == ' ') ++skip;
        }
    }
    if (chars > skip && errbuffer[skip] >= 'A' && errbuffer[skip] <= 'Z') {
        errbuffer[skip] += 'a' - 'A';
    }
    return errbuffer+skip;
}

int main(int argc, char *argv[])
{
    HANDLE proc;
    unsigned proc_id = 0;
    BOOL break_result;

    if (argc != 2) {
        printf("Usage: debugbreak process_id_number\n");
        return 1;
    }
    proc_id = (unsigned) strtol(argv[1], NULL, 0);
    if (proc_id == 0) {
        printf("Invalid process id %u\n", proc_id);
        return 1;
    }
    proc = OpenProcess(PROCESS_ALL_ACCESS, FALSE, (DWORD)proc_id);
    if (proc == NULL) {
        DWORD lastError = GetLastError();
        printf("Failed to open process %u\n", proc_id);
        printf("Error code is %lu (%s)\n", (unsigned long)lastError,
            geterrstr(lastError));
        return 1;
    }
    break_result = DebugBreakProcess(proc);
    if (!break_result) {
        DWORD lastError = GetLastError();
        printf("Failed to debug break process %u\n", proc_id);
        printf("Error code is %lu (%s)\n", (unsigned long)lastError,
            geterrstr(lastError));
        CloseHandle(proc);
        return 1;
    }
    printf("DebugBreak sent successfully to process id %u\n", proc_id);
    CloseHandle(proc);
    return 0;
}

/* END debugbreak.c */

With thanks to Kyle McKay for posting the code to the cygwin mailing list http://cygwin.com/ml/cygwin/2006-06/msg00321.html

In GDB on MinGW, how do I make Ctrl-C stop the program?

8 Answers