Where are static variables stored in C and C++?


Question

In what segment (.BSS, .DATA, other) of an executable file are static variables stored so that they don't have name collision? For example:


foo.c:                         bar.c:
static int foo = 1;            static int foo = 10;
void fooTest() {               void barTest() {
  static int bar = 2;            static int bar = 20;
  foo++;                         foo++;
  bar++;                         bar++;
  printf("%d,%d", foo, bar);     printf("%d, %d", foo, bar);
}                              }

If I compile both files and link it to a main that calls fooTest() and barTest repeatedly, the printf statements increment independently. Makes sense since the foo and bar variables are local to the translation unit.

But where is the storage allocated?

To be clear, the assumption is that you have a toolchain that would output a file in ELF format. Thus, I believe that there has to be some space reserved in the executable file for those static variables.
For discussion purposes, lets assume we use the GCC toolchain.

1
162
9/8/2018 10:30:20 PM

Accepted Answer

Where your statics go depends on if they are zero-initialized or not. zero-initialized static data goes in .BSS (Block Started by Symbol), non zero-initialized data goes in .DATA

119
2/5/2019 10:59:12 AM

When a program is loaded into memory, it’s organized into different segments. One of the segment is DATA segment. The Data segment is further sub-divided into two parts:

Initialized data segment: All the global, static and constant data are stored here.
Uninitialized data segment(BSS): All the uninitialized data are stored in this segment.

Here is a diagram to explain this concept:

enter image description here


here is very good link explaining these concepts:

http://www.inf.udec.cl/~leo/teoX.pdf


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