c++ ranges：：starts_with与C样式字符串参数有什么关系？

i7uaboj4 于 2023-03-25 发布在其他

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下面的代码打印1010

#include <iostream>
#include <range/v3/algorithm/starts_with.hpp>

int main () {
    using namespace std::literals;
    std::cout << ranges::starts_with("hello world"s, "hello"s)
              << ranges::starts_with("hello world"s, "hello")
              << ranges::starts_with("hello world",  "hello"s)
              << ranges::starts_with("hello world",  "hello") << std::endl; // prints 1010

}

为什么会这样？
我还注意到，如果两个stin相同，那么最后一个case也返回1：

std::cout << ranges::starts_with("hello world"s, "hello world"s)
              << ranges::starts_with("hello world"s, "hello world")
              << ranges::starts_with("hello world",  "hello world"s)
              << ranges::starts_with("hello world",  "hello world") << std::endl; // prints 1011

我知道std::string，比如"bla"s，是一个范围，而char[N]也是一个范围，给定一个常数N，所以我不明白为什么

c++

来源：https://stackoverflow.com/questions/75817890/what-does-rangesstarts-with-do-with-c-style-string-arguments

1条答案

按热度按时间

abithluo1#

像"hello"这样的字符串文字是一个const char[N]数组，其中N包括空终止符的空间，例如char[6] = {'h','e','l','l','o','\0'}。
像"hello"s这样的字符串文字是一个std::string对象，它在其size()中不包括空终止符。
所以，你最终得到：

starts_with("hello world"s, "hello"s) = 1
// {'h','e','l','l','o',' ','w','o','r','l','d'}
// DOES begin with
// {'h','e','l','l','o'}

starts_with("hello world"s, "hello") = 0
// {'h','e','l','l','o',' ','w','o','r','l','d'}
// DOES NOT begin with
// {'h','e','l','l','o','\0'}

starts_with("hello world",  "hello"s) = 1
// {'h','e','l','l','o',' ','w','o','r','l','d','\0'}
// DOES begin with
// {'h','e','l','l','o'}

starts_with("hello world",  "hello") = 0
// {'h','e','l','l','o',' ','w','o','r','l','d','\0'}
// DOES NOT begin with
// {'h','e','l','l','o','\0'}

starts_with("hello world"s, "hello world"s) = 1
// {'h','e','l','l','o',' ','w','o','r','l','d'}
// DOES begin with
// {'h','e','l','l','o',' ','w','o','r','l','d'}

starts_with("hello world"s, "hello world") = 0
// {'h','e','l','l','o',' ','w','o','r','l','d'}
// DOES NOT begin with
// {'h','e','l','l','o',' ','w','o','r','l','d','\0'}

starts_with("hello world",  "hello world"s) = 1
// {'h','e','l','l','o',' ','w','o','r','l','d','\0'}
// DOES begin with
// {'h','e','l','l','o',' ','w','o','r','l','d'}

starts_with("hello world",  "hello world") = 1
// {'h','e','l','l','o',' ','w','o','r','l','d','\0'}
// DOES begin with
// {'h','e','l','l','o',' ','w','o','r','l','d','\0'}

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c++ ranges：：starts_with与C样式字符串参数有什么关系？

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