Difference between File Scope and Global Scope

Question

I am a student and I am confused about global and file scope variables in C and C++. Is there any difference in both perspectives? If yes, please explain in detail.

Answer 1

A variable with file scope can be accessed by any function or block within a single file. To declare a file scoped variable, simply declare a variable outside of a block (same as a global variable) but use the static keyword.

static int nValue; // file scoped variable
float fValue; // global variable

int main()
{
    double dValue; // local variable
}

File scoped variables act exactly like global variables, except their use is restricted to the file in which they are declared.

Answer 2

It is perhaps clearer to illustrate file (or more precisely, translation unit)-scope vs global scope when there are actually multiple translation units...

Take 2 files (each being it's own translation unit, since they don't include each other)

other.cpp

float global_var = 1.0f;
static float static_var = 2.0f;

main.cpp

#include <cstdio>

extern float global_var;
//extern float static_var; // compilation error - undefined reference to 'static_var'

int main(int argc, char** argv)
{
    printf("%f\n", global_var);
}

Hence the difference is clear.