本文指在帮助需要的朋友理解链接的使用

[TOC]

环境准备

源文件 main.c

#include <stdio.h> 
int main()
{
     printf("Hello World from t1 Main!\n");
     return 0;
}

编译文件

gcc  -v main.c

生成a.out文件执行

image

编译日志为：

Apple LLVM version 10.0.1 (clang-1001.0.46.4)
Target: x86_64-apple-darwin18.6.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin
 "/Library/Developer/CommandLineTools/usr/bin/clang" -cc1 -triple x86_64-apple-macosx10.14.0 -Wdeprecated-objc-isa-usage -Werror=deprecated-objc-isa-usage -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name main.c -mrelocation-model pic -pic-level 2 -mthread-model posix -mdisable-fp-elim -fno-strict-return -masm-verbose -munwind-tables -target-sdk-version=10.14 -target-cpu penryn -dwarf-column-info -debugger-tuning=lldb -target-linker-version 450.3 -v -resource-dir /Library/Developer/CommandLineTools/usr/lib/clang/10.0.1 -isysroot /Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk -I/usr/local/include -Wno-atomic-implicit-seq-cst -Wno-framework-include-private-from-public -Wno-atimport-in-framework-header -Wno-quoted-include-in-framework-header -fdebug-compilation-dir /Users/wangshengxing/project/c/gcc/ld/src -ferror-limit 19 -fmessage-length 159 -stack-protector 1 -fblocks -fencode-extended-block-signature -fregister-global-dtors-with-atexit -fobjc-runtime=macosx-10.14.0 -fmax-type-align=16 -fdiagnostics-show-option -fcolor-diagnostics -o /var/folders/d0/z0p0y29541n_z25rrkc8c5xw0000gn/T/main-377173.o -x c main.c
clang -cc1 version 10.0.1 (clang-1001.0.46.4) default target x86_64-apple-darwin18.6.0
ignoring nonexistent directory "/Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk/usr/local/include"
ignoring nonexistent directory "/Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk/Library/Frameworks"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /Library/Developer/CommandLineTools/usr/lib/clang/10.0.1/include
 /Library/Developer/CommandLineTools/usr/include
 /Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk/usr/include
 /Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk/System/Library/Frameworks (framework directory)
End of search list.
 "/Library/Developer/CommandLineTools/usr/bin/ld" -demangle -lto_library /Library/Developer/CommandLineTools/usr/lib/libLTO.dylib -no_deduplicate -dynamic -arch x86_64 -macosx_version_min 10.14.0 -syslibroot /Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk -o a.out /var/folders/d0/z0p0y29541n_z25rrkc8c5xw0000gn/T/main-377173.o -L/usr/local/lib -lSystem /Library/Developer/CommandLineTools/usr/lib/clang/10.0.1/lib/darwin/libclang_rt.osx.a

连接文件

编译文件

执行

gcc  main.c

输出 main.o文件

初步连接

执行

ld main.o -o hello

输出

ld: warning: No version-min specified on command line
Undefined symbols for architecture x86_64:
  "_printf", referenced from:
      _main in main.o
ld: symbol(s) not found for inferred architecture x86_64

没有找到引用，说明没有找到链接库：

查看链接库

执行:

otool -L a.out

输出：

image

说明需要连接System库

image

加入System库

执行

ld   -o hello main.o -L/usr/local/lib -lSystem

输出

image

说明已经链接成功

详细参数说明

版本1

ld   -arch x86_64 -macosx_version_min 10.14.0  -o hello main.o -L/usr/local/lib -lSystem 

版本2

ld  -demangle -lto_library /Library/Developer/CommandLineTools/usr/lib/libLTO.dylib -no_deduplicate -dynamic -arch x86_64 -macosx_version_min 10.14.0 -syslibroot /Library/Developer/CommandLineTools/SDKs/MacOSX10.14.sdk -o hello main.o -L/usr/local/lib -lSystem /Library/Developer/CommandLineTools/usr/lib/clang/10.0.1/lib/darwin/libclang_rt.osx.a