使用find_first_of()和find_last_of()成员函数可以很方便地实现
一些小的功能，比如从字符串的头尾两端删除空白字符

不触动原字符串，而是返回一个新字符串
 

//: C03:Trim.h
// From "Thinking in C++, Volume 2", by Bruce Eckel & Chuck Allison.
// (c) 1995-2004 MindView, Inc. All Rights Reserved.
// See source code use permissions stated in the file 'License.txt',
// distributed with the code package available at www.MindView.net.
// General tool to strip spaces from both ends.
#ifndef TRIM_H
#define TRIM_H
#include <string>
#include <cstddef>

inline std::string trim(const std::string& s) {
  if(s.length() == 0)
    return s;
  std::size_t beg = s.find_first_not_of(" \a\b\f\n\r\t\v");
  std::size_t end = s.find_last_not_of(" \a\b\f\n\r\t\v");
  if(beg == std::string::npos) // No non-spaces
    return "";
  return std::string(s, beg, end - beg + 1);
}
#endif // TRIM_H ///:~

第1次条件判断是为了检查string是否为空；如果为空，则直接返回
原字符串的1个拷贝，不再进行其他判断

一旦找到结束点，函数就会使用开始点的位置和计算出来的子串长度
作为参数调用string类的构造函数，用来创建1个基于原字符串的新
string对象

//: C03:TrimTest.h
// From "Thinking in C++, Volume 2", by Bruce Eckel & Chuck Allison.
// (c) 1995-2004 MindView, Inc. All Rights Reserved.
// See source code use permissions stated in the file 'License.txt',
// distributed with the code package available at www.MindView.net.
#ifndef TRIMTEST_H
#define TRIMTEST_H
#include "Trim.h"
#include "../TestSuite/Test.h"

class TrimTest : public TestSuite::Test {
  enum {NTESTS = 11};
  static std::string s[NTESTS];
public:
  void testTrim() {
    test_(trim(s[0]) == "abcdefghijklmnop");
    test_(trim(s[1]) == "abcdefghijklmnop");
    test_(trim(s[2]) == "abcdefghijklmnop");
    test_(trim(s[3]) == "a");
    test_(trim(s[4]) == "ab");
    test_(trim(s[5]) == "abc");
    test_(trim(s[6]) == "a b c");
    test_(trim(s[7]) == "a b c");
    test_(trim(s[8]) == "a \t b \t c");
    test_(trim(s[9]) == "");
    test_(trim(s[10]) == "");
  }
  void run() {
    testTrim();
  }
};
#endif // TRIMTEST_H ///:~

//: C03:TrimTest.cpp {O}
// From "Thinking in C++, Volume 2", by Bruce Eckel & Chuck Allison.
// (c) 1995-2004 MindView, Inc. All Rights Reserved.
// See source code use permissions stated in the file 'License.txt',
// distributed with the code package available at www.MindView.net.
#include "TrimTest.h"

// Initialize static data
std::string TrimTest::s[TrimTest::NTESTS] = {
  " \t abcdefghijklmnop \t ",
  "abcdefghijklmnop \t ",
  " \t abcdefghijklmnop",
  "a", "ab", "abc", "a b c",
  " \t a b c \t ", " \t a \t b \t c \t ",
  "\t \n \r \v \f",
  "" // Must also test the empty string
}; ///:~

//: C03:TrimTestMain.cpp
// From "Thinking in C++, Volume 2", by Bruce Eckel & Chuck Allison.
// (c) 1995-2004 MindView, Inc. All Rights Reserved.
// See source code use permissions stated in the file 'License.txt',
// distributed with the code package available at www.MindView.net.
//{L} ../TestSuite/Test TrimTest
#include "TrimTest.h"

int main() {
  TrimTest t;
  t.run();
  return t.report();
} ///:~

可以看到，在strings型数组中字符型数组自动转换成了string对象

输出
Test "class TrimTest":
        Passed: 11      Failed: 0