Barebones code for a structured logger in C

log.h

#pragma once

// config
#define LOG_USE_STDIO 1
#define LOG_USE_FILE 0
#define LOG_USE_STRUCTURED 1

#define LOG_LEVEL_TRACE 0
#define LOG_LEVEL_WARN  1
#define LOG_LEVEL_ERROR 2

#if !defined(LOG_LEVEL)
#    define LOG_LEVEL LOG_LEVEL_TRACE
#endif


// implementation
#define LOG__EOL "\x20\x1A\n"
#define LOG__EOM "\x1A\x1A\n"

#define LOG__FLAT(file, line, level, msg) \
    level " " file ":" line " |" msg "\n"

#define LOG__STRUCTURED(file, line, level, msg) \
    level           LOG__EOL \
    "\tfile: " file LOG__EOL \
    "\tline: " line LOG__EOL \
    "\tmsg: "  msg  LOG__EOM "\n"

#if LOG_USE_STRUCTURED
#  define LOG__LINE(file, line, level, msg) \
      LOG__STRUCTURED(file, line, level, msg)
#else
#  define LOG__LINE(file, line, level, msg) \
      LOG__FLAT(file, line, level, msg)
#endif

#if LOG_USE_STDIO
#  define LOG__STDIO_FPRINTF(stream, fmt, ...) \
      fprintf(stream, fmt, __VA_ARGS__);
#else
#  define LOG__STDIO_FPRINTF(stream, fmt, ...)
#endif

#if LOG_USE_FILE
#  define LOG__FILE(stream, fmt, ...)          \
      fprintf(stream, fmt, __VA_ARGS__);        \
      fflush(stream);
#else
#  define LOG__FILE(stream, fmt, ...)
#endif

#define LOG__XSTR(x) #x
#define LOG__STR(x) LOG__XSTR(x)

#define LOG__DECL_LOGLEVELF(T, fmt, ...)           \
{                                                  \
    LOG__STDIO_FPRINTF(stdout,                     \
        LOG__LINE(__FILE__, LOG__STR(__LINE__), #T, fmt), \
            __VA_ARGS__);                          \
                                                   \
    LOG__FILE(handle,                              \
        LOG__LINE(__FILE__, LOG__STR(__LINE__), #T, fmt), \
            __VA_ARGS__);                          \
}


#if LOG_LEVEL == LOG_LEVEL_TRACE
#  define LOG_TRACEF(fmt, ...) LOG__DECL_LOGLEVELF("TRC", fmt, __VA_ARGS__);
#else
#  define LOG_TRACEF(fmt, ...)
#endif

#if LOG_LEVEL <= LOG_LEVEL_WARN
#  define LOG_WARNF(fmt, ...) LOG__DECL_LOGLEVELF("WRN", fmt, __VA_ARGS__);
#else
#  define LOG_WARNF(fmt, ...)
#endif

#if LOG_LEVEL <= LOG_LEVEL_ERROR
#  define LOG_ERRORF(fmt, ...) LOG__DECL_LOGLEVELF("ERR", fmt, __VA_ARGS__);
#else
#  define LOG_ERRORF(fmt, ...)
#endif