在地址

http://blog.csdn.net/butterfly_dreaming/article/details/10142443

中，關於trim函式的方法3：gcc編譯器不能通過問題。

       這是該程式碼：

/* 
Filename : stringTrim1.cpp
Compiler : Visual C++ 8.0
Description : Demo how to trim string by other method.
Release : 11/18/2006
*/
#include <string>
#include <iostream>
#include <cwctype>

template <class T>
std::basic_string<T>& trim(std::basic_string<T>&);

int main( ) 
{
    std::string s = " Hello World!! ";
    std::cout << s << " size:" << s.size() << std::endl;
    std::cout << trim(s) << " size:" << trim(s).size() << std::endl;

    return 0;
}

template <class T>
std::basic_string<T>& trim(std::basic_string<T>& s) 
{
    if (s.empty()) {
        return s;
  }

    std::basic_string<T>::iterator c;
    // Erase whitespace before the string

    for (c = s.begin(); c != s.end() && iswspace(*c++);); s.erase(s.begin(), --c);

    // Erase whitespace after the string

    for (c = s.end(); c != s.begin() && iswspace(*--c);); s.erase(++c, s.end());

    return s;
}
 

[[email protected] testConfig]# g++ trim.cpp
trim.cpp: In function ‘std::basic_string<_CharT, std::char_traits<_CharT>, std::allocator<_CharT> >& trim(std::basic_string<_CharT, std::char_traits<_CharT>, std::allocator<_CharT> >&)’:
trim.cpp:21: error: expected ‘;’ before ‘c’
trim.cpp:23: error: ‘c’ was not declared in this scope
trim.cpp: In function ‘std::basic_string<_CharT, std::char_traits<_CharT>, std::allocator<_CharT> >& trim(std::basic_string<_CharT, std::char_traits<_CharT>, std::allocator<_CharT> >&) [with T = char]’:
trim.cpp:11:   instantiated from here
trim.cpp:17: error: could not convert ‘s->std::basic_string<_CharT, _Traits, _Alloc>::empty [with _CharT = char, _Traits = std::char_traits<char>, _Alloc = std::allocator<char>]’ to ‘bool’
trim.cpp:21: error: dependent-name ‘std::basic_string::iterator’ is parsed as a non-type, but instantiation yields a type
trim.cpp:21: note: say ‘typename std::basic_string::iterator’ if a type is meant

這裡報的是“變數c之前丟失分號”的錯誤，這其實是個誤導性的提示，重要的提示是我劃線的這兩句。一開始很迷惑，看了這個博文

http://blog.sina.com.cn/s/blog_69d9bff30101cx8f.html

後，明白是歧義造成的。gcc編譯器並不清楚std::basic_string<T>::iterator是一種型別還是std::basic<T>的成員，除非顯示宣告其為一個型別，因此直接加上typename關鍵字就行了。下面是更正後的程式碼。

trim.cpp

#include <iostream>
#include <string>

template <typename T>
std::basic_string<T>& trim(std::basic_string<T>& s);

int main(int argc, char* []) {
	std::string str = "   	hello world    ";
	std::cout << "before:" << str << std::endl;
	trim(str);
	std::cout << "after:" << str << std::endl;
	return 0;
}

template <typename T>
std::basic_string<T>& trim(std::basic_string<T>& s) {
	if (s.empty()) {
		return s;
	}

	typename std::basic_string<T>::iterator c;//c;

	for (c = s.begin(); c != s.end() && iswspace(*c++); );
	s.erase(s.begin(), --c);

	for (c = s.end(); c != s.begin() && iswspace(*--c); );
	s.erase(++c, s.end());

	return s;
}