最近cppcheck在一些C代码中引发了一个错误,它具有以下结构：
((void)(value_prev = value),value = new_value())
在大多数情况下,这可以拆分为2行,但是在某些情况下,这在单个语句中很有用.
在实践中,我发现这适用于流行的编译器(GCC/C++lang / MSVC),它们不会发出任何警告(即使警告级别设置为最高).
示例代码：
#include <stdio.h> int get_next(int i); int main() { int i = 0,i_prev = 10; do { printf("%d\n",i); } while ((void)(i_prev = i),(i = get_next(i)) != 10); }
CppCheck 1.73(撰写本文时的最新版本)给出了以下代码的错误：
(error) Expression '(void)(i_prev=i),(i=get_next(i))!=10' depends on order of evaluation of side effects`
虽然代码可以更改为安静警告,但订单是否真的未定义？
解决方法
定义了顺序,因为它们之间存在序列点.见ISO / IEC 9899 6.5.17：
The left operand of a comma operator is evaluated as a void
expression; there is a sequence point after its evaluation. Then
the right operand is evaluated; the result has its type and value. 95)
If an attempt is made to modify the result of a comma operator or to
access it after the next sequence point,the behavior is undefined.
然后他们给出一个明确的例子：
In the function call
f(a,(t=3,t+2),c)
the function has three
arguments,the second of which has the value 5.
我不完全确定为什么CppCheck会标记它.
