去除C++String的首尾空格

时间：2010-12-05 来源：阿笨猫

string trim(string& s)

{
    const string drop = " ";
    // trim right
    s.erase(s.find_last_not_of(drop)+1);
    // trim left
    return s.erase(0,s.find_first_not_of(drop));
}

string ltrim(string& s)
{
    const string drop = " ";
    // trim left
    return s.erase(0,s.find_first_not_of(drop));
}
string rtrim(string& s)
{
    const string drop = " ";
    // trim right
    return    s.erase(s.find_last_not_of(drop)+1);

}

很多其他语言的libary都会有去除string类的首尾空格的库函数，但是标准C++的库却不提供这个功能。但是C++string也提供很强大的功能，实现trim这种功能也不难。下面是几种方法：

1.使用string的find_first_not_of,和find_last_not_of方法

/*
Filename : StringTrim1.cpp
Compiler : Visual C++ 8.0
Description : Demo how to trim string by find_first_not_of & find_last_not_of
Release : 11/17/2006
*/
#include <iostream>
#include <string>

std::string& trim(std::string &);

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;
}

std::string& trim(std::string &s)
{
    if (s.empty())
    {
        return s;
    }

    s.erase(0,s.find_first_not_of(" "));
    s.erase(s.find_last_not_of(" ") + 1);
    return s;
}

2.使用boost库中的trim,boost库对提供很多C++标准库没有但是又非常常用和好用的库函数，例如正则表达式，线程库等等。

/*
Filename : boostStringTrim.cpp
Compiler : Visual C++ 8.0 / ISO C++ (boost)
Description : Demo how to boost to trim string
Release : 02/22/2007 1.0
*/
#include <iostream>
#include <string>
#include <boost/algorithm/string.hpp>

using namespace std;
using namespace boost;

int main() {
  string s = " hello boost!! ";
  trim(s);
  cout << s << endl;
}

3.使用template（我用GCC编译不通过，用VS2005却可以）

/*
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;
}