Here's another fun fact about static array parameters in C:
Given the definition of the parameters of main in (N3220) §5.1.2.3.2, namely that:
[main] shall be defined with a return type of int and with no parameters, 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) or equivalent⁶⁾; or in some other implementation-defined manner.
⁶⁾ Thus, int can be replaced by a typedef name defined as int, or the type of argv can be written as char ** argv, or the return type may be specified by typeof(1), and so on.
--- N3220 §5.1.2.3.2 ¶1
- The value of argc shall be nonnegative.
- argv[argc] shall be a null pointer.
- If the value of argc is greater than zero, the array members argv[0] through argv[argc-1] inclusive shall contain pointers to strings, which are given implementation-defined values by the host environment prior to program startup. [...]
- If the value of argc is greater than zero, the string pointed to by argv[0] represents the program name; argv[0][0] shall be the null character if the program name is not available from the host environment. If the value of argc is greater than one, the strings pointed to by argv[1] through argv[argc-1] represent the program parameters.
- The parameters argc and argv and the strings pointed to by the argv array shall be modifiable by the program, and retain their last-stored values between program startup and program termination.
--- N3220 §5.1.2.3.2 ¶2
then assuming I've got the right interpretation of the phrase "equivalent type" (which C2y replaces with the better-defined "compatible type"), it follows that the following is (arguably, barring quibbles about formatting, and so long as one has VLA support) the most correct way to define main:
int main(int argc, char* argv[static argc + 1]) {
/* ... */
}
This makes the two biggest contracts on the values of argc and argv obvious: argv is declared as an array of pointers with at least argc+1 elements, since argv[argc] must be valid and NULL; and the size expression argc + 1 must evaluate to a positive integer, since argc must be nonnegative.
This example of the unreachable() macro from the C23 standard (N3220 §7.21.1 ¶4) agrees:
#include <stddef.h>
#include <stdio.h>
int main (int argc, char* argv[static argc + 1]) {
if (argc <= 2)
unreachable();
else
return printf("%s։ we see %s", argv[0], argv[1]);
return puts("this should never be reached");
}
As does the document N3623 "Earthly Demon XV: Definition of Main", by Martin Uecker:
5.2.2.3.2 Program startup
The function called at program startup is named main. The implementation declares no prototype for this function. It shall be defined is defined with a return type of int and with no parameters:
int main(void) { /* … */ }
or with two parameters (referred to here as argc and argv, though any names can be used, as they are local to the function in which they are declared):
int main(int argc, char *argv[static argc + 1]) { /* … */ }
or equivalent;6) or in some other implementation-defined manner. using another type that is compatible with one of these two function types, or using some other implementation-defined type.
(This wording change was accepted into C2y, starting from draft N3685, but with [static argc + 1] replaced with [], as it was before. The accompanying editor's report doesn't say why. I assume it was to avoid quibbles about VLAs.)
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