The function getenv is the only one specified by the C standard. The function putenv, and the extern environ are POSIX-specific. EDIT The main parameter envp is not specified by POSIX but is widely supported. An alternative method of accessing the environment list is to declare a third argument to the main() function: int main(int … Read more
Let’s have a look at the generated assembly of your program: .LC0: .string “Hello World…” .LC1: .string “Successfully run without main…” nomain: push rbp mov rbp, rsp mov edi, OFFSET FLAT:.LC0 call puts mov edi, OFFSET FLAT:.LC1 call puts nop pop rbp ret Note the ret statement. Your program’s entry point is determined to be … Read more
Yes, it is safe, so long as you use valid variable names. They’re local variables, so their scope doesn’t go beyond the main function. From section 5.1.2.2.1 of the C standard: The function called at program startup is named main. The implementation declares no prototype for this function. It shall be defined with a return … Read more
Yes, it is possible. If you call your program as follows: execl(“./myprog”, NULL, (char *)NULL); Or alternately: char *args[] = { NULL }; execv(“./myprog”, args); Then in “myprog”, argc will be 0. 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: 1 The … Read more
This is just main and Ctrl–Space.
Before going into the meat of the question about what is going on, it is important to point out that program is ill-formed as per defect report 1886: Language linkage for main(): […] A program that declares a variable main at global scope or that declares the name main with C language linkage (in any … Read more
In this case, history is a factor. C defined these inputs as “not constant”, and compatibility with (a good portion of) existing C code was an early goal of C++. Some UNIX APIs, such as getopt, actually do manipulate argv[], so it can’t be made const for that reason also. (Aside: Interestingly, although getopt‘s prototype … Read more
From the Ruby I’ve seen out in the wild (granted, not a ton), this is not a standard Ruby design pattern. Modules and scripts are supposed to stay separate, so I wouldn’t be surprised if there isn’t really a good, clean way of doing this. EDIT: Found it. if __FILE__ == $0 foo() bar() end … Read more
Since the question is double-tagged as C and C++, the reasoning for C++ and C would be different: C++ uses name mangling to help linker distinguish between textually identical symbols of different types, e.g. a global variable xyz and a free-standing global function xyz(int). However, the name main is never mangled. C does not use … Read more
That rule was added in the 1999 version of the C standard. In C90, the status returned is undefined. You can enable it by passing -std=c99 to gcc. As a side note, interestingly 9 is returned because it’s the return of printf which just wrote 9 characters.