CODEWITHSUNDEEP
c++stringsize
user13229658
user13229658

Reputation:

Size of string variable

I've got 2 questions:

  1. How much RAM does string variable use? Is it 28 bytes and no matter how many chars it consists of?
  2. What if length of such string is more than 28 chars? Does it take 2x more (56 bytes) or not?

Upvotes: 0

Views: 888

Answers (1)

Remy Lebeau
Remy Lebeau

Reputation: 595402

How much RAM does string variable use?

C++ has no concept of RAM. It knows only about static memory, automatic memory, and dynamic memory. How those are implemented depend on the particular details of the OS and compiler.

A string object is typically stored in automatic memory (such as on a thread's stack), unless you explicitly allocate it in dynamic memory (such as on a heap) via the new operator. If the string is a member of a class/struct that is allocated with new, but itself is not new'ed, then it is in automatic memory that just happens to be backed by dynamic memory.

Is it 28 bytes and no matter how many chars it consists of?

In any case, sizeof(string) number of bytes are allocated, which may or may not be 28 bytes, depending on the string's particular implementation. But yes, the size of a string object is fixed at compile-time and does not change at runtime, regardless of how many characters are stored inside the string.

What if length of such string is more than 28 chars? Does it take 2x more (56 bytes) or not?

A string's character data is usually allocated in dynamic memory (unless the length is small and the string implements "Short String Optimization"). The allocated size will always be the string's capacity (plus a little overhead from the string's allocator). But how much capacity is used is up to the string's particular implementation to decide. And while the capacity can grow as characters are added, how much it grows at a time is determined by the implementation.

Upvotes: 3

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