std::basic_string::npos

来自cppreference.com
< cpp‎ | string‎ | basic string

 
 
 
std::basic_string
 
static const size_type npos = -1;
这是一个特殊的值等于最大的值表示的类型size_type。依赖于上下文的确切含义,但人们普遍使用,也可以作为字符串的结束指示符期望字符串索引,或者由函数返回一个字符串索引的错误指示器的功能.
原文:
This is a special value equal to the maximum value representable by the type size_type. The exact meaning depends on context, but it is generally used either as end of string indicator by the functions that expect a string index or as the error indicator by the functions that return a string index.
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[编辑] 示例

#include <iostream>
#include <bitset>
#include <string>
 
int main()
{
    // string search functions return npos if nothing is found
    std::string s = "test";
    if(s.find('a') == std::string::npos)
        std::cout << "no 'a' in 'test'\n";
 
    // functions that take string subsets as arguments
    // use npos as the "all the way to the end" indicator
    std::string s2(s, 2, std::string::npos);
    std::cout << s2 << '\n';
 
    std::bitset<5> b("aaabb", std::string::npos, 'a', 'b');
    std::cout << b << '\n';
}

输出:

no 'a' in 'test'
st
00011