CODEWITHSUNDEEP
c++string
amigo421
amigo421

Reputation: 2537

C++ string literal type and declaration

Two types of the declaration:

char* str1 = "string 1";

and

char str2[] = "string 2";

my compiler doesn't allow me to use first declaration with a error incorrect conversion from const char[8] to char*. looks okay, the version like this:

const char* str1 = "string 1";

passed by compiler.

please clarify my understanding. I believed that if we declare both versions e.g. in main(), first one (const char*) - the only pointer will be allocated on the stack and initialized with some address in data segment. second version (char[]) - whole array of symbols will be placed on the stack

as far as I see string literal does now always have a const char[] type. is a using of const char* depricated? for C compatibility only?

where each version will store the string ?

Upvotes: 0

Views: 1469

Answers (2)

Rakete1111
Rakete1111

Reputation: 48918

char* str1 = "string 1";

This is deprecated as of C++98, and is ill-formed as of C++11, as a string literal can't be modified. Modifying it would result in undefined behavior.

To avoid this, the standard prohibits assigning it to a modifiable char pointer, as it might be modified later on without the programmer realizing that he/she shouldn't have modified it.

char str2[] = "string 2";

Yes, this allocated an array of characters, whereas each character is stored on the stack.

const char* str1 = "string 1";

This isn't deprecated, it is the recommended way (only way) to assign a string literal to a char pointer. Here, str1 is points to const chars, i.e. they can't be modified. Thus it is safe to use it somewhere, as the compiler will enforce that the chars will never be modified.

Here, str1 is stored on the stack, pointing to a string literal, which may or may not be stored in read-only memory (this is implementation defined).

Upvotes: 4

Ped7g
Ped7g

Reputation: 16586

char str2[] = "string 2";

"string 2" is string literal const char[9] stored in read-only memory.

char str2[] will allocate char array (of size deducted from initializer size) in read-write memory.

= will use the string literal to initialize the char array (doing memcpy of the "string 2" content).

I mean in principle. The actual machine code produced with optimizations may differ, setting up str2 content by less trivial means than memcpy from string literal.

char* str1 = "string 1"; - here you are trying to get the actual string literal memory address, but that one is const, so you shouldn't assign/cast it to char *.

const char* str1 should work OK, casting from const char[] to const char * is valid (they are almost the same thing, unless you have access to original array size during compilation, then the pointer variant is size-less dumb-down version).

Upvotes: 2

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