A program shall contain a global function named
main, which is the designated start of the program. It shall have one of the following forms:
|/* another implementation-defined form, with int as return type */||(3)|
|argc||-||Non-negative value representing the number of arguments passed to the program from the environment in which the program is run.|
|argv||-|| Pointer to the first element of an array of argc + 1 pointers, of which the last one is null and the previous ones, if any, point to null-terminated multibyte strings that represent the arguments passed to the program from the execution environment. If argv is not a null pointer (or, equivalently, if argc > 0), it points to a string that represents the name used to invoke the program, or to an empty string.
|body||-||The body of the main function|
argv are arbitrary, as well as the representation of the types of the parameters: int main(int ac, char** av) is equally valid.
A very common implementation-defined form of main() has a third argument (in addition to
argv), of type
char*, pointing at an array of pointers to the execution environment variables.
main function is called at program startup after initialization of the non-local objects with static storage duration. It is the designated entry point to a program that is executed in hosted environment (that is, with an operating system). The entry points to freestanding programs (boot loaders, OS kernels, etc) are implementation-defined.
The parameters of the two-parameter form of the main function allow arbitrary multibyte character strings to be passed from the execution environment (these are typically known as command line arguments), the pointers
argv .. argv[argc-1] point at the first characters in each of these strings.
argv is the pointer to the initial character of a null-terminated multibyte string that represents the name used to invoke the program itself (or an empty string "" if this is not supported by the execution environment). The strings are modifiable, although these modifications do not propagate back to the execution environment: they can be used, for example, with std::strtok. The size of the array pointed to by
argv is at least
argc+1, and the last element,
argv[argc], is guaranteed to be a null pointer.
main function has several special properties:
mainin the global namespace is reserved for functions (although it can be used to name classes, namespaces, enumerations, and any entity in a non-global namespace, except that a function called "main" cannot be declared with C language linkage in any namespace (since C++17))
mainwithout encountering a return statement, the effect is that of executing return 0;.
The manner in which the arguments given at the OS command line are converted into the multibyte character arrays referenced by
argv may involve implementation-defined processing: