A question regarding pointer

[LarryChen]

Suppose we have definitions in the following,

void foo()
{
    char s1[] = "Hello world";
}

void foo()
{
    char* s2 = new char[100];
}

What is the difference between the memory allocation space for s1 and s2?

[GeoRanger]

s1 is the static address of a 12 byte block (including the null terminator).

s2 has the size "sizeof(char *)" (likely either 4 or 8). That address will dynamically contain the address of a 100-byte block existing elsewhere.

That's why char ** x = &s2 is valid, but char ** x = &s1 will not compile.

[GeoRanger]

I should clarify. s1 is not a separate variable in your program. The 12 byte block exists and it has an address, but s1 is not declaring a separate variable to hold that address, so when you use s1 in your code the compiler directly uses the address of that 12 byte block.

In contrast, s2 is declaring a completely separate variable (namely a pointer) to hold the address you assign to it.

Thus, &s2 is valid because you have a separate variable and that variable has an address, while &s1 is not valid because s1 is the static-only address of that 12 byte block, that address is not stored in a separate variable in your program, and thus nothing exists from which "&s1" can take the address.

[nuzzle]

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