关于rfind

rfind全名reversefind

与find相反，

  size_type rfind( const basic_string &str, size_type index );
  size_type rfind( const char *str, size_type index );
  size_type rfind( const char *str, size_type index, size_type num );
  size_type rfind( char ch, size_type index );

rfind()函数:

• 返回最后一个与str中的某个字符匹配的字符，从index开始查找。如果没找到就返回string::npos
• 返回最后一个与str中的某个字符匹配的字符，从index开始查找,最多查找num个字符。如果没找到就返回string::npos
• 返回最后一个与ch匹配的字符，从index开始查找。如果没找到就返回string::npos

这里要注意与find不同的地方，rfind是从左往右数index个位置，这里作为基准index，然后从这里开始，从右往左数到第一次出现目标的位置。

find是在基准index从左往右数

例子

#include <cstring>
#include <iostream>

int main()
{
	int loc;
    std::string s = "My cat's breath smells like cat food.";

	loc = s.rfind( "breath", 8 );
	std::cout << "The word breath is at index " << loc << std::endl;
	//-1
    loc = s.rfind( "breath", 9 );
	std::cout << "The word breath is at index " << loc << std::endl;
	//9

    loc = s.rfind( "breath", 20 );
	std::cout << "The word breath is at index " << loc << std::endl;
	//9

	std::string ss = "Hi Bill, I'm ill, so please pay the bill";
	loc = ss.rfind("ill");
	std::cout << "The word breath is at index " << loc << std::endl;
	//37
	loc = ss.rfind("ill",20);
	std::cout << "The word breath is at index " << loc << std::endl;
	//13
}