用std::string::compare比较字符串大小

用std::string::compare比较字符串大小

参考见

http://www.cplusplus.com/reference/string/string/compare/

三种常见的重载形式：

int compare (const string& str) const noexcept;

int compare (size_t pos, size_t len, const string& str) const;

int compare (size_t pos, size_t len, const string& str,
             size_t subpos, size_t sublen) const;

#include <iostream>
#include <string>

int main ()
{
  std::string str1 ("green apple");
  std::string str2 ("red apple");

  if (str1.compare(str2) != 0)
    std::cout << str1 << " is not " << str2 << '\n';

  if (str1.compare(6,5,"apple") == 0)//第一个参数表示str1中的位置:str1[6],第二个参数表示要比较的字符串的最大数量,即从指定位置开始后的比较数目
    std::cout << "still, " << str1 << " is an apple\n";

  if (str2.compare(str2.size()-5,5,"apple") == 0)//同上
    std::cout << "and " << str2 << " is also an apple\n";

  if (str1.compare(6,5,str2,4,5) == 0)//str1中的“apple”和str2中的“apple”比较
    std::cout << "therefore, both are apples\n";

  return 0;
}

output如下：

green apple is not red apple
still, green apple is an apple
and red apple is also an apple
therefore, both are apples

注意：比较的结果不一定为1,0，-1，可能出现+2、-2等情况，当为正数时表示str1大于str2，为零时相等，为负数时小于str2