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I don't know c language

· 2 min read

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