c++ - 使用 boost to_lower & trim 时出现 gcc 链接器错误

Question

我尝试在我的代码中使用 boost 库，但在 Sparc Solaris 平台下出现以下链接器错误。

问题代码本质上可以概括为:

#include <boost/algorithm/string.hpp>

std::string xparam;

... 
xparam = boost::to_lower(xparam);

链接器错误是:

LdapClient.cc:349: no match for `std::string& = void' operator
/opt/gcc-3.2.3/include/c++/3.2.3/bits/basic_string.h:338: candidates are: std::basic_string<_CharT, _Traits, _Alloc>& std::basic_string<_CharT, _Traits, _Alloc>::operator=(const std::basic_string<_CharT, _Traits, _Alloc>&) [with _CharT = char, _Traits = std::char_traits<char>, _Alloc = std::allocator<char>]
/opt/gcc-3.2.3/include/c++/3.2.3/bits/basic_string.h:341:                 std::basic_string<_CharT, _Traits, _Alloc>& std::basic_string<_CharT, _Traits, _Alloc>::operator=(const _CharT*) [with _CharT = char, _Traits = std::char_traits<char>, _Alloc = std::allocator<char>]
/opt/gcc-3.2.3/include/c++/3.2.3/bits/basic_string.h:344:                 std::basic_string<_CharT, _Traits, _Alloc>& std::basic_string<_CharT, _Traits, _Alloc>::operator=(_CharT) [with _CharT = char, _Traits = std::char_traits<char>, _Alloc = std::allocator<char>]
gmake: *** [LdapClient.o] Error 1

有什么想法吗？

Answer 1

boost::to_lower不返回字符串的拷贝，它对传递给函数的变量进行操作。对于某些示例，read this .

所以不需要重新分配:

boost::to_lower(xparam);

你会得到一个错误，因为你试图将字符串分配给值 void。

如果你想复制它，使用复制版本:

std::string xparamLowered = boost::to_lower_copy(xparam);