Why does main() require braces?

问题

I tried several variations on

main() return;

or

main() if();

and obtained different errors, the most peculiar of which was

/usr/lib/gcc/i686-linux-gnu/4.4.5/../../../../lib/crt1.o: In function `_start':
(.text+0x18): undefined reference to `main'
collect2: ld returned 1 exit status

While it's uncommon for a program to require only one statement, why does main() make it a requirement to have braces?

Could someone explain why the error was so peculiar when compiling just int main();?

回答1:

Because you are defining a function named main() and a function definition is basically a function declaration (the int main() part) followed by a compound statement (the { /* ... */ } part) (you could also use a function try block, but those are very rarely used and still require braces).

You can't define any function without braces.

回答2:

It's not unique to main -- the body of any function must be surrounded by braces. Specifically §8.4/1 defines a function-body as a "compound-statement" (and, for the truly pedantic, §6.3/1 defines a compound-statement as: "{ statement-seq_opt }".

回答3:

Because it is a function. It's part of the syntax.

回答4:

Because the C++ standard says that all functions with a body must have braces. That's just the way the standard is defined, for better or for worse.

来源：https://stackoverflow.com/questions/5138609/why-does-main-require-braces