(C/C++) small helpers to generate debug logs in hairy situations

debug.h

#ifndef __DEBUG_H_INCLUDED
#define __DEBUG_H_INCLUDED

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/file.h>
#include <sys/time.h>
#include <libgen.h>
#include <time.h>
#include <errno.h>

#define __debug(msg, ...) do { \
    FILE* __f; \
    int __fd, __size, __rss, __peak; \
    int __errno; \
    char __errstr[512]; \
    char __file[512]; \
    __errno = errno; \
    __debug_get_memory_usage(&__size, &__rss, &__peak); \
    __f = fopen("/tmp/__debug.txt", "a+"); \
    if (__f) { \
        __fd = fileno(__f); \
        if (-1 != flock(__fd, LOCK_EX)) { \
            strncpy(__file, __FILE__, sizeof(__file)); \
            strncpy(__errstr, "Unknown", sizeof(__errstr)); \
            strerror_r(__errno, __errstr, sizeof(__errstr)); \
            fprintf( \
                __f, \
                "%d %s:%d/%s():\t", \
                (int)time(NULL), \
                basename(__file), \
                __LINE__, \
                __FUNCTION__ \
            ); \
            fprintf(__f, (msg), ##__VA_ARGS__); \
            fprintf(__f, \
                ", vmsize=%d, vmrss=%d, vmpeak=%d, errno=%d, errstr=\"%s\"\n", \
                __size, \
                __rss, \
                __peak, \
                __errno, \
                __errstr \
            ); \
        } \
        fclose(__f); \
    } \
} while (0)

static inline const char * const
__debug_safe_string(const char * const str)
{
    return str ? str : "--(NULL)--";
}

#define __debug_begin() __debug("BEGIN")
#define __debug_end() __debug("END")

#define __debug_stopwatch_start() do { \
    struct timeval __begin, __end; \
    struct timezone __tz; \
    const char * __custom_str; \
    __debug("Starting stopwatch", NULL); \
    gettimeofday(&__begin, &__tz); \

#define __debug_stopwatch_stop(custom_str) \
    gettimeofday(&__end, &__tz); \
    __custom_str = (custom_str); \
    __debug("Stopping stopwatch, runtime=%lu us%s%s", \
        (__end.tv_sec - __begin.tv_sec) * 1000000 \
            + __end.tv_usec - __begin.tv_usec, \
        __custom_str ? ", " : "", \
        __custom_str ? __custom_str : "", \
        NULL); \
} while (0)

static inline int
__debug_extract_number(char *str)
{
    char* num = str;
    char* end;
    for (num = str; *num && (*num < '0' || *num > '9'); ++num);
    for (end = num; *end && *end >= '0' && *end <= '9'; ++end);
    *end = '\x00';
    return atoi(num);
}

static inline void
__debug_get_memory_usage(int* const size, int* const rss, int* const peak)
{
    char str[4096];
    FILE* f;

    *size = *rss = *peak = -1;

    f = fopen("/proc/self/status", "r");
    if (!f) {
        return;
    }

    while (
        (*size == -1 || *rss == -1 || *peak == -1)
        && !feof(f)
        && fgets(str, sizeof(str), f)
    ) {
        if (*size == -1 && 0 == strncmp("VmSize:", str, 7)) {
            *size = __debug_extract_number(&str[7]);
        }
        else if (*rss == -1 && 0 == strncmp("VmRSS:", str, 6)) {
            *rss = __debug_extract_number(&str[6]);
        }
        else if (*peak == -1 && 0 == strncmp("VmPeak:", str, 7)) {
            *peak = __debug_extract_number(&str[7]);
        }
    }
    fclose(f);
}

#endif