logger.h

/**
 ****************************************************************************
 * Copyright 2015 Jonathan Barronville <[email protected]>            *
 *                                                                          *
 * Licensed under the Apache License, Version 2.0 (the "License");          *
 * you may not use this file except in compliance with the License.         *
 * You may obtain a copy of the License at                                  *
 *                                                                          *
 *     http://www.apache.org/licenses/LICENSE-2.0                           *
 *                                                                          *
 * Unless required by applicable law or agreed to in writing, software      *
 * distributed under the License is distributed on an "AS IS" BASIS,        *
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. *
 * See the License for the specific language governing permissions and      *
 * limitations under the License.                                           *
 ****************************************************************************
 */

#pragma once

#include <assert.h>
#include <stdarg.h>
#include <stddef.h>
#include <stdio.h>
#include <string.h>
#include <time.h>

#define PROGRAM_NAME "blah"

// @jonathanmarvens' very simple logger generation macro.
#define GENERATE_LOGGER(log_level) \
  void \
  blah_log_##log_level(char const * log_format_string, ...) { \
    /* Get the current time. */ \
    time_t const time_ = time(NULL); \
    /* Convert the raw time into a ISO 8601 date and time-formatted string. */ \
    char formatted_date[21]; /* YYYY-MM-DDThh:mm:ssZ (20 + '\0') */ \
    assert(strftime(formatted_date, (sizeof formatted_date), "%Y-%m-%dT%TZ", \
      gmtime(&time_)) != 0); \
    /* Log! */ \
    fprintf(stderr, "[%s] [%s] [%s]\n", PROGRAM_NAME, #log_level, formatted_date); \
    size_t const log_format_string_length = strlen(log_format_string); \
    char log_format_string_2[((int) log_format_string_length) + 2]; \
    log_format_string_2[0] = '\0'; \
    strncat(log_format_string_2, log_format_string, log_format_string_length); \
    strncat(log_format_string_2, "\n", (size_t) 1); \
    va_list extra_arguments; \
    va_start(extra_arguments, log_format_string); \
    vfprintf(stderr, log_format_string_2, extra_arguments); \
    va_end(extra_arguments); \
  }

GENERATE_LOGGER(debug) // blah_log_debug
GENERATE_LOGGER(error) // blah_log_error
GENERATE_LOGGER(info) // blah_log_info
GENERATE_LOGGER(warn) // blah_log_warn

E.g.:

blah_log_info("Opening up document: \"%s\".", "wat.txt");