Gcc warning: suggest parentheses around assignment used as truth value [-Wparentheses]

/*Snip from gcc manual */

-Wparentheses
Warn if parentheses are omitted in certain contexts, such as when there is an
assignment in a context where a truth value is expected, or when operators are
nested whose precedence people often get confused about.
Also warn if a comparison like x<=y<=z appears; this is equivalent to (x<=y ? 1
: 0) <= z, which is a different interpretation from that of ordinary mathematical
notation.
Also warn for dangerous uses of the GNU extension to ?: with omitted middle
operand. When the condition in the ?: operator is a boolean expression, the
omitted value is always 1. Often programmers expect it to be a value computed
inside the conditional expression instead.
This warning is enabled by ‘-Wall’.

讲人话，举个例子：

#include <stdio.h>
 
int main(void)
{
    int a = 1;
    int b = 2;
    if (a = b)
    {
        //do nothing
    }
 
    return 0;
}
        在gcc下使用-Wall选项编译，出现告警：

       warning: suggest parentheses around assignment used as truth value [-Wparentheses]

       虽然在判断的语句里使用赋值是很普遍的，例如经典的指针操作语句while(*s++ = *t++)（也会出现告警），但更普遍的现象是人们在使用“=”的时候，明明是想用“==”作比较而非赋值。

       因此，gcc编辑器在-Wall选项下，会明确用户在判断语句中使用“=”的真正意图。有一天，你会庆幸gcc编译器提醒你这个问题。

       当你想在判断语句中使用“=”时，要加上括号：       

if ((a = b) != 0)
          或者

if ((a = b)) （推荐这种方式）
      这样子就可以消除安全隐患，gcc也不会报告警了。