data section in C++

Question

I have a question to clarify my confusion about the memory organization in computer in C++.

In C++, different data is put in different location. My understanding is like this.

1) data segment section, where global and static data are located;

2) heap section, the objects created by new

3) stack section, the local variable

4) text section, the code itself.

Is that right? Is there anything I missed or did wrong?

Thanks!

Answer 1

I wrote an article called "C++ Internals :: Memory Layout" which will clarify this for you.

Short excerpt from the article:

.text segment

It's a Read-Only, fixed-size segment.

The text segment, a.k.a. code segment, contains executable instructions provided by the compiler and assembler.

.data segment

It's a Read-Write, fixed-size segment.

The data segment, a.k.a. initialized data segment, contains initialized:

• global variables (including global static variables)
• static local variables.

The segment's size depends on the size of the values in the source code, the values can be altered at run-time.

.rdata/.rodata segment

It's a Read-Only segment

The segments contains static unnamed data (like string constants)

.bss segment

It's a Read-Write and adjacent to the .data segment.

BSS segment, a.k.a. uninitialized data segment, contains statically-allocated (global and static) variables represented solely by zero-valued bits on program start. BSS stands for Block Started by Symbol, a pseudo-operation that existed in a very old assembler developed for the IBM.

heap & stack

You are quite right about those. Anyway, if you want to check some examples and get a closer look, please, refer to mentioned article.

Answer 2

There are typically at least two data sections. One with initialized globals, another without (BSS). A stack section isn't typically emitted in the binary.

Of course, these kind of very implementation specific questions are kinda useless if you don't specify the implementation.