I am trying to get a signal name to print when getting a signal number. I actually have :

char* getsig(int sig){
    switch (sig)
    case SIGKILL:
        return "SIGKILL";
    case SIGSTOP:
        return "SIGSTOP";
    case SIGTERM:
        return "SIGTERM";
    case SIGTRAP:
        return "SIGTRAP";
    case SIGABRT:
        return "SIGABRT";
    case SIGALRM:
        return "SIGALARM";
    case SIGSEGV:
        return "SIGSEGV";
    case SIGQUIT:
        return "SIGQUIT";
    case SIGINT:
        return "SIGINT";
    case SIGCHLD:
        return "SIGCHLD";
    case SIGCONT:
        return "SIGCONT";
    case SIGPIPE:
        return "SIGPIPE";
    case SIGFPE:
        return "SIGFPE";
    case SIGILL:
        return "SIGILL";
    case 0:
        return "[NO SIGNAL TO DELIVER]";
        return "UNKN";

I can see that this is wrong : I have no certitude that those char* names will be stored in data section on every compiler. I am certain that there is a clean way of doing such a thing, but I cannot find it on the internet. Do anyone has an idea of how I could do this task the beautiful way?


The final aim is to print a potential signal delivered by a ptrace(PTRACE_CONT, ...); call, e.g: printf("ptrace(PTRACE_CONT); [delivered %s]\n", getsig(data));


1 Answer 1


The way to do this in C is to define an array, and use designated array initializers to ensure the correct mapping between number and string, like so:

static const char *signames[] = {
    [0] = "[NO SIGNAL TO DELIVER]",

const char *getsig(int sig) {
    if (sig < 0 || sig >= sizeof(signames) / sizeof(*signames) || !signames[sig])
        return "UNKN";

    return signames[sig];

Note that it is hard to make this portable; the list of available signals varies by operating system, and some don't even have the concept of signals. Some operating systems and/or standard libraries might already have some function to convert signal numbers to strings, if you target a specific platform and don't care about compatibility, you might consider using that.

Note that strsignal() should be available on any POSIX platform, although it gives you a more human readable string like "Killed" instead of "SIGKILL".


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