When I include a static library "libupnpx.a" in my project that is 6 MB, does this make my app 6 MB larger? - static-libraries

Question

I have heard the compiler strips out unused code. But when I include a libupnpx.a static library archive of 6 MB, will this make app 6 MB larger? Or is this same as including the library source code directly?

Answer 1

The answer is not as simple as you may think:
Let's do an experiment:
We will create a libfoo.a with the following structure:
Makefile:
LIBOUT=libfoo.a
SRC=foo1.c foo2.c foo3.c
OBJ=$(SRC:%.c=%.o)
default: test1 test2 test3
test1: $(LIBOUT)
$(CC) -o $# test1.c -L. -lfoo
test2: $(LIBOUT)
$(CC) -o $# test2.c -L. -lfoo
test3: $(LIBOUT)
$(CC) -o $# test3.c -L. -lfoo
$(LIBOUT): $(OBJ)
$(AR) ruv $(LIBOUT) $(OBJ)
foo1.c:
#include <stdio.h>
int foo1_service_a() {
printf("Performing foo1_service_a\n");
return 0;
}
foo2.c:
#include <stdio.h>
int foo2_service_a() {
printf("Performing foo2_service_a\n");
return 0;
}
foo3.c:
#include <stdio.h>
int foo3_service_a() {
printf("Performing foo3_service_a\n");
return 0;
}
int foo3_service_b() {
printf("Performing foo3_service_b\n");
return 0;
}
And three test programs:
test1.c:
int main() {
foo1_service_a();
return 0;
}
test2.c:
int main() {
foo2_service_a();
return 0;
}
test3.c:
int main() {
foo3_service_a();
return 0;
}
When we compile them we get:
-rw-r--r-- 1 masud users 285 Aug 3 16:42 Makefile
-rw-r--r-- 1 masud users 96 Aug 3 16:38 foo1.c
-rw-r--r-- 1 masud users 1496 Aug 3 16:39 foo1.o
-rw-r--r-- 1 masud users 97 Aug 3 16:39 foo2.c
-rw-r--r-- 1 masud users 1496 Aug 3 16:39 foo2.o
-rw-r--r-- 1 masud users 173 Aug 3 16:39 foo3.c
-rw-r--r-- 1 masud users 1688 Aug 3 16:40 foo3.o
-rw-r--r-- 1 masud users 5008 Aug 3 16:40 libfoo.a
-rwxr-xr-x 1 masud users 9132 Aug 3 16:43 test1
-rw-r--r-- 1 masud users 45 Aug 3 16:43 test1.c
-rwxr-xr-x 1 masud users 9132 Aug 3 16:43 test2
-rw-r--r-- 1 masud users 45 Aug 3 16:43 test2.c
-rwxr-xr-x 1 masud users 9251 Aug 3 16:43 test3
-rw-r--r-- 1 masud users 45 Aug 3 16:43 test3.c
As you can tell that each of test1 test2 and test3 have foo1.o; foo2.o and foo3.o dictating their end sizes.
So it's the archive's content division that determines the size of the end binary.
Exercise for the reader
What happens to the sizes when you strip the binaries? do test1 test2 and test3 become the same size?
Why or why not ? :)

Answer 2

You can generally expect that static linking and "including the library source code directly" will have equivalent impacts on the size of the resulting executable. There are be some minor cases in which this may not be strictly true, but generally speaking, they should be approximately equivalent.