C 语言中关于顺序点（Sequence points）的问题

本文详细介绍了C语言中的顺序点(sequence point)概念及其在标准中的定义。通过具体示例展示了违反顺序点规则可能导致的未定义行为，强调了使用-Wsequence-point选项检查潜在问题的重要性。

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关于顺序点(sequence point)，在C标准中有解释，不过很晦涩。

The sequence points laid down in the Standard are the following:

The point of calling a function, after evaluating its arguments.
The end of the first operand of the && operator.
The end of the first operand of the || operator.
The end of the first operand of the ?: conditional operator.
The end of the each operand of the comma operator.
Completing the evaluation of a full expression. They are the following:
- Evaluating the initializer of an auto object.
- The expression in an ‘ordinary’ statement—an expression followed by semicolon.
- The controlling expressions in do , while , if , switch or for statements.
- The other two expressions in a for statement.
- The expression in a return statement.

我们在平时编码中尽量避免写出与实现相关、受实现影响的代码便是了。而-Wsequence-point选项恰恰可以帮我们这个忙，它可以帮我们查出这样的代码来，并给出其警告。
e.g.
/* * test_sequence_point.c * gcc -Wsequence-point test_sequence_point.c */ ＃i nclude int main() { int i = 12; i = i--; printf("the i is %d/n", i); return 0; }
gcc -Wsequence-point test_sequence_point.c
test_sequence_point.c: In function `main':
test_sequence_point.c:10: warning: operation on `i' may be undefined
在两个平台上给出的编译警告都是一致的，但是输出结果却大相径庭。

Solaris输出：
the i is 11
Windows输出：
the i is 12
类似的像这种与顺序点相关的代码例子有：

i = i++; a = b[i++] a[i++] = i printf(" *p++ = %c, *(p+1) = %c, *p = %c/n", *(p+1),*p++,*p);

这样子的代码往往不能按照你所想像的结果输出，所以这样子的情况尽量避免吧。

等等...

引用 http://publications.gbdirect.co.uk/c_book/chapter8/sequence_points.html