- A static variable inside a function keeps its value between invocations.
- A static global variable or a function is "seen" only in the file it's declared in
(1) is the more foreign topic if you're a newbie, so here's an example:
#include <stdio.h>
void foo()
{
int a = 10;
static int sa = 10;
a += 5;
sa += 5;
printf("a = %d, sa = %d\n", a, sa);
}
int main()
{
int i;
for (i = 0; i < 10; ++i)
foo();
}
This prints:
a = 15, sa = 15
a = 15, sa = 20
a = 15, sa = 25
a = 15, sa = 30
a = 15, sa = 35
a = 15, sa = 40
a = 15, sa = 45
a = 15, sa = 50
a = 15, sa = 55
a = 15, sa = 60
This is useful for cases where a function needs to keep some state between invocations, and you don't want to use global variables. Beware, however, this feature should be used very sparingly - it makes your code not thread-safe and harder to understand.
(2) Is used widely as an "access control" feature. If you have a .c file implementing some functionality, it usually exposes only a few "public" functions to users. The rest of its functions should be made static, so that the user won't be able to access them. This is encapsulation, a good practice.
Quoting Wikipedia:
In the C programming language, static
is used with global variables and
functions to set their scope to the
containing file. In local variables,
static is used to store the variable
in the statically allocated memory
instead of the automatically allocated
memory. While the language does not
dictate the implementation of either
type of memory, statically allocated
memory is typically reserved in data
segment of the program at compile
time, while the automatically
allocated memory is normally
implemented as a transient call stack.
And to answer your second question, it's not like in C#.
In C++, however, static is also used to define class attributes (shared between all objects of the same class) and methods. In C there are no classes, so this feature is irrelevant.
Does your DLL project have any actual exports? If there are no exports, the linker will not generate an import library .lib file.
In the non-Express version of VS, the import libray name is specfied in the project settings here:
Configuration Properties/Linker/Advanced/Import Library
I assume it's the same in Express (if it even provides the ability to configure the name).
Best Answer
The 'compile mode' setting that you are referring to is the setting for the runtime library that gets linked with whatever library or executable you produce.
If your project is set up to produce a DLL (check the main project page), then it'll still produce a DLL no matter what you're putting into the runtime library setting. What I think you want to do is change the setting on the DLL's main project page from DLL to Static Library instead of changing the runtime library setting.
Once you've done this, make sure that both the executable and library projects have the same runtime library setting (the /MT switch you refer to), otherwise you'll get tons of strange error messages if the linker is trying to match up two different runtime libraries in the same executable.