我在使用 xcode 4.6.2 中的 clang++ 在 mac os x 10.8.3 下编译带有“-std=c++11 -stdlib=libc++”的程序时遇到问题。
当我尝试使用 std::mem_fn() 或（已弃用）std::mem_fun_ref() 时，我收到链接器错误“未找到符号”。在 c++03 标准下，相同的代码（使用 std::mem_fun_ref 而不是 std::mem_fn）编译和链接没有任何问题。
如果我在对象上调用相同的成员函数而不通过 mem_fn 或 mem_fun_ref 引用它，则程序编译并运行没有任何问题。这是一个clang++问题，一个mac os问题，还是我做错了什么？
编码：
#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;
int main(int argc, char **arvc)
{
/* The beginning of the function compiles without any errors */
string str = "It's a test)";
if (str.empty())
{
cout << "String is empty!!!" << endl;
}
vector<string> v1;
v1.push_back("str1");
v1.push_back("str2");
v1.push_back("");
v1.push_back("str4");
v1.push_back("");
v1.push_back("str6");
/* The code after this point leads to linker error */
vector<string>::iterator it = remove_if(v1.begin(), v1.end(), mem_fn(&string::empty));
v1.erase(it, v1.end());
for (it = v1.begin(); it < v1.end(); ++it)
{
cout << " '" << *it << "'" << endl;
}
return 0;
}
编译日志：
$ xcrun clang++ -v -std=c++11 -stdlib=libc++ ../src/test_cxx.cpp
Apple LLVM version 4.2 (clang-425.0.28) (based on LLVM 3.2svn)
Target: x86_64-apple-darwin12.3.0
Thread model: posix
"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang" -cc1 -triple x86_64-apple-macosx10.8.0 -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -main-file-name test_cxx.cpp -pic-level 2 -mdisable-fp-elim -masm-verbose -munwind-tables -target-cpu core2 -target-linker-version 136 -v -resource-dir /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/clang/4.2 -isysroot / -fmodule-cache-path /var/folders/nz/0x05d6p14gddzxxn8ymnn74c0000gn/T/clang-module-cache -stdlib=libc++ -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /Volumes/Work/projects/web/sp3/build -ferror-limit 19 -fmessage-length 80 -stack-protector 1 -mstackrealign -fblocks -fobjc-runtime=macosx-10.8.0 -fobjc-dispatch-method=mixed -fobjc-default-synthesize-properties -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -o /var/folders/nz/0x05d6p14gddzxxn8ymnn74c0000gn/T/test_cxx-kAQ3wk.o -x c++ ../src/test_cxx.cpp
clang -cc1 version 4.2 based upon LLVM 3.2svn default target x86_64-apple-darwin12.3.0
ignoring nonexistent directory "/usr/include/c++/v1"
#include "..." search starts here:
#include <...> search starts here:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1
/usr/local/include
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/clang/4.2/include
/usr/include
/System/Library/Frameworks (framework directory)
/Library/Frameworks (framework directory)
End of search list.
"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/ld" -demangle -dynamic -arch x86_64 -macosx_version_min 10.8.0 -syslibroot / -o a.out /var/folders/nz/0x05d6p14gddzxxn8ymnn74c0000gn/T/test_cxx-kAQ3wk.o -lc++ -lSystem /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/clang/4.2/lib/darwin/libclang_rt.osx.a
Undefined symbols for architecture x86_64:
"std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >::empty() const", referenced from:
_main in test_cxx-kAQ3wk.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)