Where are static variables stored (in C/C++)?
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.
Where your statics go depends on if they are 0 initialized or not. 0 initialized static data goes in .BSS (Block Started by Symbol), non 0 initialized data goes in .DATA
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:
here is very good link explaining these concepts:
http://www.inf.udec.cl/~leo/teoX.pdf
In fact, a variable is tuple (storage, scope, type, address, value):
storage : where is it stored, for example data, stack, heap...
scope : who can see us, for example global, local...
type : what is our type, for example int, int*...
address : where are we located
value : what is our value
Local scope could mean local to either the translational unit (source file), the function or the block depending on where its defined. To make variable visible to more than one function, it definitely has to be in either DATA or the BSS area (depending on whether its initialized explicitly or not, respectively). Its then scoped accordingly to either all function(s) or function(s) within source file.
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