CODEWITHSUNDEEP
c++unixepoll
trvecvlt
trvecvlt

Reputation: 102

epoll and negative errno value

I have ERROR_OUT function, which uses vfprintf inside to log errors in console. When im trying to log some epoll errors with this function ERROR_OUT(L_NOTICE, "Epoll error: %d", errno); , i'm getting strange output sometimes:

Epoll error: -1079274856

I'm using it after epoll_wait and epoll_ctl only and it's beeing called only in case of negative return value.

Code of ERROR_OUT: 

void ERROR_OUT(int level, char *template, ...){           
    va_list ap;
    va_start(ap, template);

    if ( level <= verbosity ){
                if (output_handler == NULL){
                        vfprintf(stderr, template, ap);
                }else{
                        (*output_handler)(level, template, ap);
                }
    }
    va_end(ap);
}

Code of output handler:

void log_both(int level, const char *fmt, ...){
    va_list argp;
    va_start(argp, fmt);   
    vfprintf(stderr, fmt, argp);
    printf("\n");
    if (globalArgs.db_verbosity >= level)
        globalArgs.db_log->log_error(format(fmt, argp));
    va_end(argp);
}

Upvotes: 1

Views: 255

Answers (1)

foobar
foobar

Reputation: 606

You pass a va_list in the call to log_both via *output_handler and wrap that va_list in the va_list named argp.

So you actually pass a va_list that contains a va_list to vfprintf as third argument which expects a decimal due to %d to be the first element in the va_list.

It should therefore be void log_both(int level, const char *fmt, va_list argp){} with va_list argp;, va_start(argp, fmt); and va_end(argp); removed from the function body.

void log_both(int level, const char *fmt, va_list argp){
    vfprintf(stderr, fmt, argp);
    printf("\n");
    if (globalArgs.db_verbosity >= level)
        globalArgs.db_log->log_error(format(fmt, argp));
}

Upvotes: 1

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