[SOLVED] g++ -o command not working

jovin555 · 06-07-2015, 04:18 AM

I am trying to do the first example of advanced linux programming.pdf.In page 30,there is an example.I have compiled the code.But when i try to execute the command

g++ -o reciprocal main.o reciprocal.o

I am getting the following errors

main.o: In function `main':
main.c

.text+0x25): undefined reference to `reciprocal'
collect2: error: ld returned 1 exit status

these are my files.
main.c

Code:

#include <stdio.h>
#include "reciprocal.hpp"

int main(int argc,char **argv)
{
	int i;
	i = atoi(argv[1]);
	printf("The reciprocal of %d is %g\n",i,reciprocal(i));
	return 0;
}

reciprocal.cpp

Code:

#include <cassert>
#include "reciprocal.hpp"

double reciprocal (int i){
//i should be non-zero
assert(i!=0);
return 1.0/i;
}

reciprocal.hpp

Code:

#ifdef _cplusplus
extern 'C'{
#endif

extern double reciprocal(int i);

#ifdef _cplusplus
}
#endif

Please let me know what is wrong with this command execution

NevemTeve · 06-07-2015, 05:50 AM

Try this:

Code:

g++ -o reciprocal main.c reciprocal.c

a4z · 06-07-2015, 06:46 AM

Quote:

Originally Posted by jovin555

g++ -o reciprocal main.o reciprocal.o

I am getting the following errors

main.o: In function `main':
main.c

.text+0x25): undefined reference to `reciprocal'
collect2: error: ld returned 1 exit status

main needs stuff from reciprocal so the linker must see reciprocal first

change the order to g++ -o reciprocal reciprocal.o main.o

jovin555 · 06-07-2015, 11:53 AM

Quote:

main needs stuff from reciprocal so the linker must see reciprocal first

change the order to g++ -o reciprocal reciprocal.o main.o

I tried this command and got the same error.

When i tried the other suggestion,

Quote:

g++ -o reciprocal main.c reciprocal.c

I got the following error.

Code:

main.c: In function ‘int main(int, char**)’:
main.c:7:18: error: ‘atoi’ was not declared in this scope

NevemTeve · 06-07-2015, 12:08 PM

my bad: you don't have main.c and recefice.c only main.cpp and recefice.cpp:

Code:

g++ -o reciprocal main.cpp reciprocal.cpp

if the problem persists, add the missing include into main.cpp:

Code:

#include <cstdlib>

PS: if you do have 'main.c' then rename it to 'main.cpp'

jovin555 · 06-07-2015, 12:14 PM

I have main.c,reciprocal.cpp and reciprocal.hpp as i have mentioned these with the code at start of the thread.

I have included the "#include <cstdlib>" file in my main.c.
but when compiling that gives me error.

Code:

main.c:3:21: fatal error: cstdlib.h: No such file or directory
compilation terminated.

The name of the pdf that i am following is
Advanced Linux Programming - Richard Esplin

NevemTeve · 06-07-2015, 01:13 PM

Please read the last sentence of my previous post.

NevemTeve · 06-07-2015, 01:22 PM

Please don't think C and C++ are freely interchangeable synonyms; they are different programming languages.
From C++ you can call C, from C you are not to call C++ (it might or mightn't work).

jovin555 · 06-08-2015, 09:39 AM

I have tried changing main.c to main.cpp.When i compile using command

g++ -c main.cpp

i am getting the following errors

main.cpp: In function ‘int main(int, char**)’:
main.cpp:7:18: error: ‘atoi’ was not declared in this scope

NevemTeve · 06-08-2015, 09:47 AM

I've already suggested adding this line into main.cpp:

Code:

#include <cstdlib>

jovin555 · 06-08-2015, 11:10 AM

After adding #include <cstdlib> to the main.cpp file,it worked well.
Thanks NevemTeve for your help.

NevemTeve · 06-08-2015, 12:24 PM

You are welcome.