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Why, if I write
int main() { //... } do I not need to write return 0; at the end of the main function? Does the compiler do it for me?
I use GCC / C99.
596
return 0: A return 0 means that the program will execute successfully and did what it was intended to do. return 1: A return 1 means that there is some error while executing the program, and it is not performing what it was intended to do.
Short Answer: Nothing. Better Answer: return 0 it's used in main like a signal for know the exit of program was a success when return 0 executes. Best Answer: Still nothing because compilers already "put" return 0 in the the end of your code if you not explicit.
The main function is generally supposed to return a value and after it returns something it finishes execution. The return 0 means success and returning a non-zero number means failure. Thus we "return 0" at the end of main function.
Basically, yes. Functions are not required to return anything, even if they declare a return type other than void . The value returned will be undefined.
C99 and C++ special case the main function to return 0 if control reaches the end without an explicit return. This only applies to the main function.
The relevant bit of the C99 spec is 5.1.2.2.3 for the main special case
5.1.2.2.3 Program termination
If the return type of the main function is a type compatible with int, a return from the initial call to the main function is equivalent to calling the exit function with the value
returned by the main function as its argument; reaching the}that terminates the main function returns a value of 0.6.9.1/12
If the
}that terminates a function is reached, and the value of the function call is used by the caller, the behavior is undefined.
You can test this out with gcc:
int foo ( void ) { } int main( void ) { } C89 mode ( errors for both functions ):
sandiego:$ gcc src/no_return.c -std=c89 -Wall src/no_return.c: In function ‘main’: src/no_return.c:2: warning: control reaches end of non-void function src/no_return.c: In function ‘foo’: src/no_return.c:1: warning: control reaches end of non-void function C99 mode ( main is a special case ) :
sandiego:$ gcc src/no_return.c -std=c99 -Wall src/no_return.c: In function ‘foo’: src/no_return.c:1: warning: control reaches end of non-void function If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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