未定义的对 `mysql_init' 的引用

2022-01-11 00:00:00 c linker c++

我正在尝试在我的新服务器上编译我的程序，但目前它不适合我.

I am trying to compile my program on my new server, but it's not working for me at the moment.

错误日志是:

rasmus@web01:~/c++$ make test
g++ `mysql_config --cflags --libs` main.cpp logger.cpp cpulogger.cpp -o test
/tmp/ccPaMZUy.o: In function `CPULogger':
/home/rasmus/c++/cpulogger.cpp:7: undefined reference to `mysql_init'
/home/rasmus/c++/cpulogger.cpp:8: undefined reference to `mysql_real_connect'
/home/rasmus/c++/cpulogger.cpp:10: undefined reference to `mysql_get_client_info'
/tmp/ccPaMZUy.o: In function `~CPULogger':
/home/rasmus/c++/cpulogger.cpp:16: undefined reference to `mysql_close'
collect2: ld returned 1 exit status
make: *** [all] Error 1

如您所见，我正在针对 MySQL 进行编译 - 我已检查 mysql.h 是否存在于包含路径中.

As you can see I am compiling against MySQL - I have checked that mysql.h is present in include paths.

我错过了什么?

cpulogger.cpp 在顶部有 #include "cpulogger.h"，然后 cpulogger.h 有这个:

cpulogger.cpp has #include "cpulogger.h" at the top, then cpulogger.h has this:

#include <iostream>
#include <fstream>
#include <mysql/mysql.h>

编译器不会抱怨缺少mysql/mysql.h，所以那部分一定可以工作吗?

The compiler does not complain about missing mysql/mysql.h, so that part must work?

rasmus@web01:~/c++$ mysql_config --cflags --libs
-I/usr/include/mysql -DBIG_JOINS=1  -fno-strict-aliasing  -g
-L/usr/lib -lmysqlclient -lpthread -lz -lm -lrt -ldl

生成文件:

all:
    g++ `mysql_config --cflags --libs` main.cpp logger.cpp cpulogger.cpp -o test


test: all
    ./test

这是一个全新的 Ubuntu 服务器安装，上面安装了 mysql-server.

It's a fresh Ubuntu server installation with a mysql-server install on it.

[已解决]:

将链接器库放在编译器命令的末尾是可行的.

Putting linker libraries at the end of the compiler commands works.

all:
    g++ main.cpp logger.cpp cpulogger.cpp -o test `mysql_config --cflags --libs`

请参阅下面的答案以获得解释.

See answer below for explanation.

推荐答案

链接器的参数顺序很重要.使用 mysql-config after 列出需要它的文件.链接器将看到 cpulogger.o 需要 mysql_init 并在其后列出的库中查找符号.如果这些库在参数中较早列出，则不会再次搜索它们.

The order of arguments to the linker is significant. Use mysql-config after listing the files that need it. The linker will see that cpulogger.o needs mysql_init and look in libraries listed after it for the symbol. If the libraries were listed earlier in the arguments they won't be searched again.

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