zlog

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A reliable, high-performance, thread safe, flexsible, clear-model, pure C logging library.

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A reliable, high-performance, thread safe, flexsible, clear-model, pure C logging library.

zlog

zlog is a reliable, high-performance, thread safe, flexible, clear-model, pure C logging library.

Actually, in the C world there was NO good logging library for applications like logback in java or log4cxx in c++. Using printf can work, but can not be redirected or reformatted easily. syslog is slow and is designed for system use. So I wrote zlog. It is faster, safer and more powerful than log4c. So it can be widely used.

1. Install

Downloads: https://github.com/HardySimpson/zlog/releases

bash

tar -zxvf zlog-latest-stable.tar.gz
cd zlog-latest-stable/

zlog can be built either with CMake or with the plain makefile. Both produce the same shared and static libraries, the zlog-chk-conf tool and a pkg-config file.

1.1 CMake

Needs CMake 3.12 or newer.

bash

cmake -DCMAKE_BUILD_TYPE=Release -B build
cmake --build build -j8
sudo cmake --install build

CMAKE_INSTALL_PREFIX says where it goes, /usr/local by default. The GNU install directories are honoured, so distributions that keep their libraries in lib64 can ask for that:

bash

cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/opt/zlog -DCMAKE_INSTALL_LIBDIR=lib64 -B build

Configure with -DUNIT_TEST=ON to build the test suite, which ctest then runs:

bash

cmake -DUNIT_TEST=ON -B build
cmake --build build -j8
ctest --test-dir build

Besides the usual Debug and Release, the build types Tsan and Asan build the library and the tests under the thread and address sanitizers. See doc/developer.md.

1.2 Makefile

bash

make
sudo make install

bash

make PREFIX=/usr/local/
sudo make PREFIX=/usr/local/ install

PREFIX indicates the installation destination for zlog, and LIBRARY_PATH the library directory under it (lib by default, so pass LIBRARY_PATH=lib64 where that is the convention).

1.3 After installing

Refresh your dynamic linker to make sure your program can find the zlog library.

bash

$ sudo vi /etc/ld.so.conf
/usr/local/lib
$ sudo ldconfig

Before running a real program, make sure libzlog.so is in the directory where the system's dynamic lib loader can find it. The command metioned above are for linux. Other systems will need a similar set of actions.

2. Configuration file

There are 3 important concepts in zlog: categories, formats and rules.

Categories specify different kinds of log entries. In the zlog source code, category is a zlog_category_t * variable. In your program, different categories for the log entries will distinguish them from each other.

Formats describe log patterns, such as: with or without time stamp, source file, source line.

Rules consist of category, level, output file (or other channel) and format. In brief, if the category string in a rule in the configuration file equals the name of a category variable in the source, then they match. Still there is complex match range of category. Rule decouples variable conditions. For example, log4j must specify a level for each logger(or inherit from father logger). That's not convenient when each grade of logger has its own level for output(child logger output at the level of debug, when father logger output at the level of error)

Now create a configuration file. The function zlog_init takes the files path as its only argument.

bash

$ cat /etc/zlog.conf

[formats]
simple = "%m%n"
[rules]
my_cat.DEBUG    >stdout; simple

In the configuration file log messages in the category my_cat and a level of DEBUG or higher are output to standard output, with the format of simple %m - usermessage %n - newline. If you want to direct out to a file and limit the files maximum size, use this configuration

config

my_cat.DEBUG            "/var/log/aa.log", 1M; simple

3. Using zlog API in C source file

3.1 Sample code

bash

$ vi test_hello.c

#include <stdio.h> 

#include "zlog.h"

int main(int argc, char** argv)
{
    int rc;
    zlog_category_t *c;

    rc = zlog_init("/etc/zlog.conf");
    if (rc) {
    printf("init failed\n");
    return -1;
    }

    c = zlog_get_category("my_cat");
    if (!c) {
    printf("get cat fail\n");
    zlog_fini();
    return -2;
    }

    zlog_info(c, "hello, zlog");

    zlog_fini();

    return 0;
}

3.2 Compile, and run it

bash

$ cc -c -o test_hello.o test_hello.c -I/usr/local/include
$ cc -o test_hello test_hello.o -L/usr/local/lib -lzlog -lpthread
$ ./test_hello
hello, zlog

Both builds install a pkg-config file, so the flags above can also be queried:

bash

$ cc -o test_hello test_hello.c $(pkg-config --cflags --libs zlog)

Add --static when linking against libzlog.a, so that the private dependencies are pulled in as well.

The CMake build also installs a package config, so a CMake project can just ask for zlog:

cmake

find_package(zlog REQUIRED)
target_link_libraries(test_hello PRIVATE zlog::zlog)

zlog::zlog_s is the static library. Both targets carry the include directory and the thread flags, so nothing else needs setting.

4. Advanced Usage

syslog model, better than log4j model
log format customization
multiple output destinations including static file path, dynamic file path, stdout, stderr, syslog, user-defined output
runtime manually or automatically refresh configure(safely)
high-performance, 250'000 logs/second on my laptop, about 1000 times faster than syslog(3) with rsyslogd
user-defined log level
thread-safe and process-safe log file rotation
microsecond accuracy
dzlog, a default category log API for easy use
MDC, a log4j style key-value map
self debuggable, can output zlog's self debug&error log at runtime
No external dependencies, just based on a POSIX system and a C99 compliant vsnprintf.