I don't know c language

allocate string by array or pointer

What’s difference between them?

#include<stdio.h>

int main()
{

char a[] = “apple”; char *b = “apple”;

}

Answer

char a[] = "apple";

When string is allocated by array, all the characters are saved in the stack.

char *b = "apple";

When string is allocated by pointer, only pointer is saved in the stack, and it points to the string, which is saved in the read-only section.

function argument array or pointer

What’s difference between them?

#include<stdio.h>

void func1(char * s)
{
	printf("%s",s);
}
void func2(char s[])
{
	printf("%s",s);
}
int main()
{
	func1("apple");
	func2("apple");

return 0;

}

In book “The c programming language 2nd”

As formal parameters in a function definition,

char s[];

and

char *s;

are equivalent; we prefer the latter because it says more explicitly that the parameter is a pointer

But in which situation, we prefer to use array argument? In one mail to linux kernel mentioned that

https://lkml.org/lkml/2015/9/3/499

The “array as function argument” syntax is occasionally useful (particularly for the multi-dimensional array case), so I very much understand why it exists, I just think that in the kernel we’d be better off with the rule that it’s against our coding practices.

sizeof is an operator

sizeof value is determined in compile time.

sizeof is only correctly used in two places.

array

char s[10];
printf("%zu",sizeof(s));
// 10

type

char* s="hello";
printf("%zu",sizeof(s));
printf("%zu",sizeof(char *));
/*
8
8
*/
// sizeof(variable) == sizeof(variable type)

https://en.wikipedia.org/wiki/Sizeof