CMAKE_CXX_FLAGS中的标志"-l"不起作用 [英] Flag '-l' in CMAKE_CXX_FLAGS doesn't work

问题描述

我在Mac机器上编写了一些代码，它运行良好，但是当我将其移植到Linux机器时，我得到了undefined reference to curl_easy_init

I have some code I wrote on my mac machine and it has been working perfectly but when I port it over to a Linux machine I get an undefined reference to curl_easy_init

我的编译器标志包括用于链接的-lcurl.

My compiler flags include a -lcurl for linking.

这是我的链接方式:

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -L/curl/lib/dir -lcurl")

我尝试过使用-L/curl/lib/dir

此计算机上已安装卷曲:

Curl is installed on this machine:

$ curl --version
curl 7.47.0 (x86_64-pc-linux-gnu) libcurl/7.47.0 GnuTLS/3.4.10 zlib/1.2.8 libidn/1.32 librtmp/2.3
Protocols: dict file ftp ftps gopher http https imap imaps ldap ldaps pop3 pop3s rtmp rtsp smb smbs smtp smtps telnet tftp 
Features: AsynchDNS IDN IPv6 Largefile GSS-API Kerberos SPNEGO NTLM NTLM_WB SSL libz TLS-SRP UnixSockets 

推荐答案

从不将-l标志添加到 CMAKE_EXE_LINKER_FLAGS ，此外还添加到 CMAKE_CXX_FLAGS (标志-l用于链接器，而不用于编译器).

Never add -l flags to CMAKE_EXE_LINKER_FLAGS and moreover to CMAKE_CXX_FLAGS (the flag -l is for the linker, not for a compiler).

要与图书馆建立链接，请使用 target_link_libraries :专为此目的:

For link with libraries use target_link_libraries: it is specifically intended for that purpose:

target_link_libraries(<your-executable> curl)

---

将标记添加到*_FLAGS变量时，该标记会在链接器的命令行中的源文件之前(实际上是目标文件)之前添加.如果源文件使用库中的某些功能，则链接器无法找到它.

---

When you add a flag to *_FLAGS variable, the flag is added before the source file (object file actually) in the linker's command-line. If the source file uses some function from the library, then the linker cannot find it.

相反，在链接器的命令行中，在源文件后后添加了由命令target_link_libraries生成的标志.

As opposite, a flag produced by command target_link_libraries is added after the source file in the linker's command line.

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