<?=运算符C ++大于问号等于符号 [英] <?= operator C++ greater less question mark equals sign

问题描述

我看到在代码中使用了<?=和>?=: http://community.topcoder.com/stat? c = problem_solution& rm = 151152& rd = 5854& pm = 2923& cr = 310333

I saw <?= and >?= used in a code: http://community.topcoder.com/stat?c=problem_solution&rm=151152&rd=5854&pm=2923&cr=310333

我试图在没有包含文件的情况下进行编译，以测试它是否是标准文件，但没有用.然后，我添加了包含，但仍然会出现相同的错误:

I tried to compile without the includes to test if it's standard, but it didn't work. I then added the includes, but it still gives the same error:

question-mark.cpp:15:5:错误:?"之前的预期主表达式 令牌问题mark.cpp:15:6:错误:预期的主要表达式 在"="令牌问号.cpp:15:9之前:错误:预期在:"之前 ‘;’令牌问题-mark.cpp:15:9:错误:预期的主要表达式 在;"令牌之前

question-mark.cpp:15:5: error: expected primary-expression before ‘?’ token question-mark.cpp:15:6: error: expected primary-expression before ‘=’ token question-mark.cpp:15:9: error: expected ‘:’ before ‘;’ token question-mark.cpp:15:9: error: expected primary-expression before ‘;’ token

#include <stdio.h>
#include <algorithm> 
#include <iostream> 
#include <sstream> 
#include <string> 
#include <vector> 

using namespace std;

int main()
{

    int x = 3;
    int y = 2;
    x >?= y;
    printf("x = %d\n", x);

    return 0;
}

以下是链接中的代码中使用它的方式:

Here's how it is used in the code from the link:

x <?= h[i][j];  // x = (h[i][j] < x) ? h[i][j] : x;

我该如何进行这项工作?

How can I make this work?

推荐答案

这些是GCC扩展程序运算符. a <?= b的含义与a = min(a, b)相同(>?=是"max"运算符)，但是它只计算一次左侧表达式.当a是变量时，这并不重要，但是当a表示表达式时，尤其是在表达式具有副作用时，这可能会有所不同.例如，在

These are GCC extensions operators. a <?= b has the same meaning as a = min(a, b) (>?= is the "max" operator), but it evaluates its left-hand side expression only once. This is not important when a is a variable, but it may make a difference when a represents an expression, especially when the expression has a side effect. For example, in

*dest++ <?= *src++;

dest++中的++仅被评估一次.

两个运算符现在都已已弃用.

这篇关于&lt;?=运算符C ++大于问号等于符号的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！