在函数参数列表中声明char指针和char数组有什么区别？

Question

What is the difference between

foo(char* grid){}

And

foo(char grid[]){}

I have a program that I tested on both styles of the function parameters. It seemed to work, but why does it work? What is the difference? Which one is more efficient, and is the first one passing by reference?

Answer 1

In the case of a function parameter (and only in that case), they mean the same thing.

Note that C99 dropped the "implicit int " rule, so your examples should be something like:

void foo(char* grid){}

and

void foo(char grid[]){}

A parameter defined with an array type is "adjusted" to become a parameter of pointer type, pointing to the the element type of the array.

Reference: N1570 6.7.6.3 paragraph 7. (This is a freely available draft of the 2011 ISO C standard, PDF, 1.7 MB.)

(In all other contexts, a pointer declaration and an array declaration are different. See section 6 of the comp.lang.c FAQ .

All parameters in C are passed by value, not by reference. In this case, the value being passed happens to be a pointer value, which is the address of a char object. For example, if you write:

char arr[10];
func(arr);

then the value being passed is &arr[0] (there's a separate language rule that says that array expressions are converted/adjusted to become pointer expressions in most but not all contexts). Note that no information about the length of the array is passed; if you want to keep track of that, you'll have to do so explicitly.

C doesn't have pass-by-reference as a language feature. Passing a pointer value is a way to emulate pass-by-reference.