A program shall contain a global namespace function namedmain, which is the designated start of the program in hosted environment. It shall have one of the following forms:

[edit]Explanation

Themain function is called at program startup afterinitialization of the non-local objects with staticstorage duration. It is the designated entry point to a program that is executed inhosted environment (that is, with an operating system). The entry points tofreestanding programs (boot loaders, OS kernels, etc) are implementation-defined.

The parameters of the two-parameter form of themain function allow arbitrary multibyte character strings to be passed from the execution environment (these are typically known ascommand line arguments), the pointers[argv[1], argv[argc-1]] point at the first characters in each of these strings.argv[0] (if non-null) 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, withstd::strtok. The size of the array pointed to byargv is at leastargc+1, and the last element,argv[argc], is guaranteed to be a null pointer.

Themain function has the following several special properties:

Themain function has several restrictions (violation of which renders the program ill-formed):

[edit]Notes

If themain function is defined with afunctiontry block, the exceptions thrown by the destructors of static objects (which are destroyed by the impliedstd::exit) are notcaught by it.

The manner in which the arguments given at the OS command line are converted into the multibyte character arrays referenced byargv may involve implementation-defined processing:

• Parsing C++ Command-Line Arguments MSDN
• Shell Introduction POSIX

A very common implementation-defined form ofmain() has a third argument (in addition toargc andargv), of typechar**, pointing atan array of pointers to the execution environment variables.

[edit]Example

#include <cstdlib>#include <iomanip>#include <iostream> int main(int argc,char*argv[]){std::cout<<"argc == "<< argc<<'\n'; for(int ndx{}; ndx!= argc;++ndx)std::cout<<"argv["<< ndx<<"] == "<<std::quoted(argv[ndx])<<'\n';std::cout<<"argv["<< argc<<"] == "<<static_cast<void*>(argv[argc])<<'\n'; /* ... */ return argc==3?EXIT_SUCCESS:EXIT_FAILURE;// optional return value}

argc == 3argv[0] == "./convert"argv[1] == "table_in.dat"argv[2] == "table_out.dat"argv[3] == 0

[edit]References

[edit]Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit]See also

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