Help With Static Libraries?

Dark dude · #1 03-Sep-2007, 07:32

So, basically, I'm writing a test static library + application in Dev-C++ in order to understand how I can get it to function properly, however, despite endless google searching for 6 hours flat, nothing has helped.

The library contains a single function which takes an integer parameter, and returns that integer multiplied by 5. The actual application gets an integer from the user, and passes it to the function in the library, and then prints out the result.

The actual result is the following:

The source is as follows:

Static Library (Sum.a):

main.c:

CPP / C++ / C Code:

#include <stdio.h>

#include "sum.h"

int Sum(int i)
{
    return i * 5;
}

sum.h:

CPP / C++ / C Code:

int Sum(int i);

Test Application [test.exe]:

main.cpp:

CPP / C++ / C Code:

#include <stdio.h>
#include <stdlib.h>

#include "sum.h"

int main()
{
  int sumnum;
  scanf("%d",sumnum);
  sumnum = Sum(sumnum);
  printf("%d",sumnum);
  system("PAUSE");	
  return 0;
}

My compile logs, incase they're of any help, are as follows:

Sum.a

Quote:

Compiler: Default compiler
Building Makefile: "C:\Dev-Cpp\Projects\Tests\Makefile.win"
Executing make...
make.exe -f "C:\Dev-Cpp\Projects\Tests\Makefile.win" all
g++.exe -c main.c -o main.o -I"C:/Dev-Cpp/lib/gcc/mingw32/3.4.2/include" -I"C:/Dev-Cpp/include/c++/3.4.2/backward" -I"C:/Dev-Cpp/include/c++/3.4.2/mingw32" -I"C:/Dev-Cpp/include/c++/3.4.2" -I"C:/Dev-Cpp/include"
ar r Sum.a main.o
ar: creating Sum.a
ranlib Sum.a

Execution terminated

Test.exe

Quote:

Compiler: Default compiler
Building Makefile: "C:\Dev-Cpp\Projects\Tests\Makefile.win"
Executing make...
make.exe -f "C:\Dev-Cpp\Projects\Tests\Makefile.win" all
g++.exe -c main.cpp -o main.o -I"C:/Dev-Cpp/lib/gcc/mingw32/3.4.2/include" -I"C:/Dev-Cpp/include/c++/3.4.2/backward" -I"C:/Dev-Cpp/include/c++/3.4.2/mingw32" -I"C:/Dev-Cpp/include/c++/3.4.2" -I"C:/Dev-Cpp/include"
g++.exe main.o -o "test.exe" -L"C:/Dev-Cpp/lib" Sum.a

Execution terminated
Compilation successful

Anybody know what's going on? I've gone through a library worth of information online to no avail (excuse the pun).

Thanks,
~Dark Dude~

#2 03-Sep-2007, 09:58

Here is a complete, working example of using a static library.

CPP / C++ / C Code:

// static_main.cpp
#include <iostream>

using namespace std;

#include <static_lib.h>

int main()
{
    int a = 3, b = 4, c = 0;
    c = add( a, b );
    cout << a << " + " << b << " = " << c << endl;
    return 0;
}

CPP / C++ / C Code:

// static_lib.h

#ifdef __cplusplus
extern "C"
{
#endif

int add( int a, int b );

#ifdef __cplusplus
}
#endif

CPP / C++ / C Code:

// static_lib.h

#ifdef __cplusplus
extern "C"
{
#endif

int add( int a, int b );

#ifdef __cplusplus
}
#endif

Code:

# Makefile for creating static libraries

CC 			= g++
CPPFLAGS	= -Wall -W -pedantic
INC			= -I.
LIBPATH		= .
LIBNAME		= static_lib
OBJS		= $(LIBNAME).o 
LIBOUT		= lib$(LIBNAME).a	
TEST		= static_main
AR			= ar
ARFLAGS		= -rsv

all: clean $(TEST)

$(TEST): $(OBJS) $(LIBOUT)
	$(CC) $(CPPFLAGS) $(INC) -o $(TEST) $(TEST).cpp -L$(LIBPATH) -l$(LIBNAME)

$(LIBNAME).o:
	$(CC) $(CPPFLAGS) $(INC) -c $(LIBNAME).cpp

$(LIBOUT): $(LIBNAME).o
	$(AR) $(ARFLAGS) $(LIBOUT) $(OBJS) 

clean:
	rm -rf $(LIBOUT) $(OBJS) $(TEST)

Output of invoking gmake:

Code:

rm -rf libstatic_lib.a   static_lib.o  static_main
g++ -Wall -W -pedantic -I. -c static_lib.cpp
ar -rsv libstatic_lib.a  static_lib.o
ar: creating libstatic_lib.a
a - static_lib.o
g++ -Wall -W -pedantic -I. -o static_main static_main.cpp -L. -lstatic_lib

Output of executing static_main:

Code:

3 + 4 = 7

Note that only very minor differences to the Makefile should be required for those who are using Windoze.

:davis:

davekw7x · #3 03-Sep-2007, 10:18

Quote:

Originally Posted by Dark dude

So, basically, I'm writing a test static library...+

I suggest that before putting a function into a library that you test the function in a "regular" program.

Here is the function in a C program:

CPP / C++ / C Code:

#include <stdio.h>
#include <stdlib.h>

int Sum(int i)
{
    return i * 5;
}

int main()
{
    int sumnum;
    scanf("%d", sumnum);
    sumnum = Sum(sumnum);
    printf("%d", sumnum);
    system("PAUSE");
    return 0;
}

If you get a seg fault here, as I did, you know that the problem is with either the main() function or the Sum() function, and not due to some procedural error in putting the function into a library.

I also suggest that you change project settings so that you turn on compiler warnings.

If I compile with -Wall -W -pedantic, the compiler tells me:

Code:

gcc -Wall -W -pedantic    test.c   -o test
test.c: In function ‘main’:
test.c:12: warning: format ‘%d’ expects type ‘int *’, but argument 2 has type ‘int’

Running the program gives me a segfault.

Fix the function. Thoroughly test the function. Then see what you have to do to get it into a library.

This is a trivial function, so testing it is also trivial.

Generally speaking, testing library functions is extremely important. Of course testing is always important, and of course, in general, you can't necessarily prove a function is correct just by testing. But, generally speaking, testing is easier (more time-effective) if you test it before going through the steps of putting it into a library.

Regards,

Dave

Dark dude · #4 03-Sep-2007, 10:25

Edit: Solved it with help of both previous posters

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Help With Static Libraries?

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