g++ question

[bo01]

Hello
I searched it but didn't find an answer.

I compile and run some programs in c++ with g++ and I use the flag -lpq in order to manage the build a program that uses an external library (database lib).

My question is what exactly does this (or these?) flag/s? First of all, I think -lpq is not one argument but I don't know (and I cannot find it) what -l does or -p or -pq or -q...

Is it so obvious???

THANX in advance

[Catalyst2Death]

I think (someone correct me) that the -lpq option refers to libpq. This flag tells the linker that it needs code from the libpq library.

[bo01]

Thank u Catalyst.
So its one flag and not two or three together in one? Can u be more specific? Why is this flag necessary as I have included the library in my program?
Thanks again

[pansz]

-lpq means link (-l) the libpq.a or libpq.so library, which should be in the library search path specified by -L

man gcc should give you everything detail.

[snova]

So its one flag and not two or three together in one? Can u be more specific? Why is this flag necessary as I have included the library in my program?

Short answer; there are headers, and then there are libraries. You need both.

#include merely makes the library available to you by exposing its interface, but you need to link the library in before the finished program can actually use the code. This is what -lpq is for- it specifies a library to be linked in.

[bo01]

Thanks a lot guys. Its clear now!