是的argv [N]写吗？

问题描述

C11 5.1.2.2.1 / 2说：

C11 5.1.2.2.1/2 says:

参数 ARGC 和的argv 和琴弦由的argv 阵列应
  是可修改的程序，并保留程序之间的最后存储的值
  启动和终止程序。

这个我间pretation是：它规定：

My interpretation of this is that it specifies:

int main(int argc, char **argv)
{
    if ( argv[0][0] )
        argv[0][0] = 'x';   // OK

    char *q;
    argv = &q;              // OK
}

但它并没有说任何事情：

however it does not say anything about:

int main(int argc, char **argv)
{
    char buf[20];
    argv[0] = buf;
}

是的argv [0] = BUF; 允许

我可以看到（至少）两个可能的参数：

I can see (at least) two possible arguments:

• 特意提到以上报价的argv 和的argv [X] [Y] 而不是的argv [X] ，这样的意图是，它是不可修改


• 的argv 是一个指向非 - 常量对象，所以在没有具体的措辞相反我们应该假设他们是可以修改的对象。

• The above quote deliberately mentioned argv and argv[x][y] but not argv[x], so the intent was that it is not modifiable
• argv is a pointer to non-const objects, so by in the absence of specific wording to the contrary, we should assume they are modifiable objects.

推荐答案

IMO，code像的argv [1] =123; 是UB

IMO, code like argv[1] = "123"; is UB.

参数argc和argv与琴弦由argv数组指出，应
  是可修改的程序，并保留程序之间的最后存储的值
  启动和终止程序。C11dr§5.1.2.2.12

回想一下，常量多年后，C'S创作走进℃。

Recall that const came into C many years after C's creation.

就像的char * s =ABC; 是有效的，当它应该是为const char * s =ABC; 。不需要进行必要常量其他太多现有的code将引进常量的被打破

Much like char *s = "abc"; is valid when it should be const char *s = "abc";. The need for const was not required else too much existing code would have be broken with the introduction of const.

同样，即使的argv 今天应该算是 char * const的的argv [] 或常量，缺乏在字符常量的* argv的[] 未完成指定常量的-ness需求的argv ，的argv [] 或的argv [] [] 。在常量 -ness需求将需要通过规范来驱动。

Likewise, even if argv today should be considered char * const argv[] or some other signature with const, the lack of const in the char *argv[] does not complete specify the const-ness needs of the argv, argv[], or argv[][]. The const-ness needs would need to be driven by the spec.

从我读，因为规范是在这个问题上沉默，这是UB。

From my reading, since the spec is silent on the issue, it is UB.

未定义行为，否则该国际标准的文字''未定义行为'或行为的任何明确定义§42

：

的main（）是一个非常特殊的功能是什么C.允许的是在其他功能上可能会或可能不会在被允许的main（）。的C规格细节的属性有关它的参数，鉴于签署 INT ARGC，CHAR *的argv [] 不应该需要。 的main（），不像用C等功能，可以有一个备用签名 INT主要（无效）和潜在的其他人。 的main（）不是折返。像C规格超出它的方式来详细说一下可以修改： ARGC ，的argv ，的argv [] [] ，它是合理的问题，如果的argv [] 是可以修改的，因为它从规范声称$ C遗漏$ C能。

main() is a very special function is C. What is allowable in other functions may or may not be allowed in main(). The C spec details attributes about its parameters that given the signature int argc, char *argv[] that shouldn't need. main(), unlike other functions in C, can have an alternate signature int main(void) and potentially others. main() is not reentrant. As the C spec goes out of its way to detail what can be modified: argc, argv, argv[][], it is reasonable to question if argv[] is modifiable due to its omission from the spec asserting that code can.

鉴于专业的main（）并指定遗漏了的argv [] 的修改，保守程序员把这个作为greyness UB，有待未来的C规格说明。

Given the specialty of main() and the omission of specifying that argv[] as modifiable, a conservative programmer would treat this greyness as UB, pending future C spec clarification.

如果的argv [I] 是修改一个给定的平台上，肯定的范围I 不应该超过 ARGC-1 。

If argv[i] is modifiable on a given platform, certainly the range of i should not exceed argc-1.

由于 ARGV [ARGC] 应是一个空指针，assignining ARGV [ARGC] 其他东西比 NULL 似乎是违反

As "argv[argc] shall be a null pointer", assignining argv[argc] to something other than NULL appears to be a violation.

虽然字符串修改，code不应超过原始字符串的长度。

Although the strings are modifiable, code should not exceed the original string's length.

char *newstr = "abc";
if (strlen(newstr) <= strlen(argv[1]))
  strcpy(argv[1], newstr);

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