需要左值作为条件运算符中赋值的左操作数 [英] lvalue required as left operand of assignment in conditional operator

问题描述

#include <stdio.h>
int main()
{
        int a = 1, b;
        a ? b = 3 : b = 4;
        printf("%d, %d", a, b);
        return 0;
}

[user@localhost programs]$ gcc -Wall vol.c
vol.c: In function ‘main’:
vol.c:5:16: error: lvalue required as left operand of assignment
  a ? b = 3 : b = 4;
                ^

我给定的左值是 b 那么为什么 gcc 显示错误以及如何解决？

I have given lvalue as b then why gcc is showing error and how to fix it?

推荐答案

它与操作员排序有关。编译器认为您正在做什么

It has to do with operator sequencing. What the compiler thinks you're doing is

(a ? b = 3 : b) = 4

这显然是不正确的。

相反，为什么不把 b 在左侧，并仅使用条件表达式获取要分配的值，例如

Instead, why not put the b on the left side, and get only the value to assign using the conditional expression, like

b = a ? 3 : 4;

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