blocks|key|2373943|text|是的，因为在函数调用之前和之后都有一个序列点。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2373944|§本标准的1.0.17条规定：|2373945|2373946|调用函数时(无论函数是否为内联函数)，在对所有函数参数(如果有)求值之后，在函数体中执行任何表达式或语句之前都会有一个序列点。在复制返回值之后和在函数外部执行任何表达式之前也有一个序列点)。|blockquote|2373947|2373948|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|L|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|M|8|@]|9|@]|A|$]]|$1|E|3|F|5|G|7|N|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|P|8|@]|9|@]|A|$]]]|J|$]]

Yes, because there is a sequence point before and after function calls.

§1.0.17 of the Standard says:

<blockquote>
 When calling a function (whether or not the function is inline), there
 is a sequence point after the evaluation of all function arguments (if
 any) which takes place before execution of any expressions or
 statements in the function body. There is also a sequence point after
 the copying of a returned value and before the execution of any
 expressions outside the function).
</blockquote>

blocks|key|418474|text|没有。在这种情况下，标准确实是模棱两可的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|418475|如果你想确认这一点，gcc有一个非常酷的选项-Wsequence-point，在这种情况下，它会警告你，操作可能是未定义的|offset|length|style|CODE|418476|entityMap^0|0|M|G|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@$D|L|E|M|F|G]]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

No there isn't. The standard is indeed ambiguous in this case.

If you want to confirm that, gcc has this really cool option <code>-Wsequence-point</code> and in this case it will warn you that the operation may be undefined

blocks|key|4273992|text|有一个序列点，但是外部函数的参数的计算顺序(及其副作用)仍然是未定义的。该实现可以自由地首先计算内部的f()，使用它的副作用x=1，或者使用它的副作用x=2计算第二个参数。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|4273993|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

There is a sequence point, but the order of evaluation (and their side effects) of the outer function's arguments is still undefined. The implementation is free to first evaluate the inner f(), with its side effect x=1, or the second argument with its side effect x=2.

blocks|key|420259|text|是的，由于逗号操作符错误，将有一个序列点，但结果仍将是未定义的，因为函数参数的求值未定义，因此无法预测此表达式将generate........means未定义的行为的值是什么|type|unstyled|depth|inlineStyleRanges|entityRanges|data|420260|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Yes there will be a sequence point due to comma operatror But still result will be undefined as evaluation of function arguments is undefined so can't predict what value this expression will generate........means undefined behaviour

blocks|key|2374097|text|在函数调用的开头和结尾都有序列点。但是，因为函数参数上的操作顺序是由实现定义的，所以不能保证f(x=1,1)将在x=2之前执行。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2374098|还要注意，函数调用中的,不是引入序列点的逗号运算符。|2374099|entityMap^0|1A|8|1K|3|0|B|1|0^^$0|@$1|2|3|4|5|6|7|J|8|@$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|R|8|@]|D|@]|E|$]]]|I|$]]

There are sequence points at the beginning of a function call and at it's end. However because the order of operations on function arguments is implementation defined you can't gaurantee that <code>f(x=1,1)</code> will be executed before <code>x=2</code>.

Also note that the <code>,</code> in the function call case is not the comma operator that introduces a sequence point.

blocks|key|420329|text|the+(draft)+standard+6.5.2.2，10中的相关引用是：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|420330|420331|未指定函数指示符、实际参数和子表达式在实际参数中的求值顺序，但在实际调用之前有一个序列点。|blockquote|420332|420333|420334|因此，对于您的表达式，第一个参数(特别是对f的调用)可以在第二个参数之前进行计算；例如：|style|CODE|420335|(x+=+1,+1),+f+<sp>+call,+(x+=+2),+f+<sp>+call|code-block|syntax|javascript|420336|或者，可以在第二个参数之后对其求值；例如：|420337|(x+=+2),+(x+=+1,+1),+f+<sp>+call,+f+<sp>+call|420338|函数调用本身可以(并且很可能会)包含更多的序列点(特别是如果它包含一条return语句)。|420339|根据这一点，赋值之间是否存在序列点。这取决于平台(“未指明”)。|420340|由于在第二种情况下，您在两个序列点之间为x赋值两次，因此您在这样的平台上具有未定义的行为。|420341|entityMap|0|LINK|mutability|MUTABLE|url|http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf^0|0|K|0|0|0|0|0|0|L|1|0|0|0|0|Z|6|0|0|K|1|0^^$0|@$1|2|3|4|5|6|7|1A|8|@]|9|@$A|1B|B|1C|1|1D]]|C|$]]|$1|D|3|-4|5|6|7|1E|8|@]|9|@]|C|$]]|$1|E|3|F|5|G|7|1F|8|@]|9|@]|C|$]]|$1|H|3|-4|5|6|7|1G|8|@]|9|@]|C|$]]|$1|I|3|-4|5|6|7|1H|8|@]|9|@]|C|$]]|$1|J|3|K|5|6|7|1I|8|@$A|1J|B|1K|L|M]]|9|@]|C|$]]|$1|N|3|O|5|P|7|1L|8|@]|9|@]|C|$Q|R]]|$1|S|3|T|5|6|7|1M|8|@]|9|@]|C|$]]|$1|U|3|V|5|P|7|1N|8|@]|9|@]|C|$Q|R]]|$1|W|3|X|5|6|7|1O|8|@$A|1P|B|1Q|L|M]]|9|@]|C|$]]|$1|Y|3|Z|5|6|7|1R|8|@]|9|@]|C|$]]|$1|10|3|11|5|6|7|1S|8|@$A|1T|B|1U|L|M]]|9|@]|C|$]]|$1|12|3|-4|5|6|7|1V|8|@]|9|@]|C|$]]]|13|$14|$5|15|16|17|C|$18|19]]]]

The relevant quote from <a href="http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf" rel="nofollow">the (draft) standard</a> [6.5.2.2, 10] is:

<blockquote>
 The order of evaluation of the function designator, 
 the actual arguments, and subexpressions within the 
 actual arguments is unspecified, but there is a sequence 
 point before the actual call.
</blockquote>

So for your expression, the first argument (in particular the call to <code>f</code>) could be
evaluated before the second argument; e.g.:

<pre><code>(x = 1, 1), f &lt;sp&gt; call, (x = 2), f &lt;sp&gt; call
</code></pre>

Or, it could be evaluated after the second argument; e.g.: 

<pre><code>(x = 2), (x = 1, 1), f &lt;sp&gt; call, f &lt;sp&gt; call
</code></pre>

[The function call itself can (and most probably will) contain more sequence points (in particular if it contains a <code>return</code> statement).]

Depending on that, there is a sequence point between the assignments or not. 
It is up to the platform ("unspecified").

Since in the 2nd case, you are assigning to <code>x</code> twice between two sequence points, you have undefined behaviour on such a platform.

Is there a sequence point between the two assignments in the following code:

<pre><code>f(f(x=1,1),x=2);
</code></pre>

Is there a sequence point between these assignments?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

文章

问答

视频

学习中心

腾讯云实验室

直播

竞赛

腾讯云代码分析专区

腾讯iOA零信任安全管理系统专区

腾讯云架构师技术同盟交流圈

腾讯云数据库专区

腾讯云顾问专区

腾讯云原生专区

腾讯混元专区

腾讯云TCE专区

腾讯云Lighthouse专区

腾讯云HAI专区

腾讯云Edgeone专区

腾讯云存储专区

腾讯云智能专区

腾讯轻联专区 

腾讯云开发专区

TAPD专区

腾讯轻量云游戏服专区

腾讯云最具价值专家

腾讯云架构师技术同盟

腾讯云创作之星

腾讯云开发者先锋

腾讯云代码助手

云原生构建

TAPD 敏捷项目管理

Cloud Studio

SDK中心

API中心

命令行工具

涵盖代码开发、场景应用、自动测试全流程，助你从零构建专属AI助手

一站式MCP教程库，解锁AI应用新玩法

以下代码中的两个赋值之间是否存在序列点：f(f(x=1,1),x=2);

问这些赋值之间是否存在序列点？
EN

Stack Overflow用户

社区

活动

圈层

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问这些赋值之间是否存在序列点？EN