在POSIX系统上argc可以为零吗?

问题描述

给出主程序的标准定义:

Given the standard definition for the main program:

int main(int argc, char *argv[]) {
   ...
}

在什么情况下POSIX系统上argc可以为零?

Under which circumstances can argc be zero on a POSIX system?

推荐答案

是的，有可能.如果您按以下方式调用程序:

Yes, it is possible. If you call your program as follows:

execl("./myprog", NULL, (char *)NULL);

或者:

char *args[] = { NULL };
execv("./myprog", args);

然后在"myprog"中，argc将为0.

Then in "myprog", argc will be 0.

标准也专门允许关于主机环境中程序启动的第5.1.2.2.1节中所述的0 argc:

The standard also specifically allows for a 0 argc as noted in section 5.1.2.2.1 regarding program startup in a hosted environment:

int main(void) { /* ... */ } 

或具有两个参数(此处称为argc和argv，尽管可以使用任何名称，因为它们是本地名称 到声明它们的函数):

or with two parameters (referred to here as argc and argv, though any names may be used, as they are local to the function in which they are declared):

int main(int argc, char *argv[]) { /* ... */ }

或同等学历；或以其他一些实现定义的方式.

or equivalent; or in some other implementation-defined manner.

2 如果已声明，则main函数的参数应遵循以下约束:

2 If they are declared, the parameters to the main function shall obey the following constraints:

• argc的值应为非负数.
• argv[argc]应为空指针.

• The value of argc shall be nonnegative.
• argv[argc] shall be a null pointer.

...

还请注意，这意味着如果argc为0，则保证argv[0]为NULL.但是，在标准中没有明确说明printf在用作%s说明符的参数时如何处理NULL指针.在这种情况下，许多实现都将输出(null)"，但我不认为这是可以保证的.

Note also that this means that if argc is 0 then argv[0] is guaranteed to be NULL. How printf treats a NULL pointer when used as the argument to a %s specifier is not spelled out in the standard however. Many implementations will output "(null)" in this case but I don't believe it's guaranteed.

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