Met undefined reference when use glib in ubuntu - glib

Question

I've searched about this a lot. And tried a lot. Just don't know where I go wrong.
Here is my code, it's very simple:
#include <glib.h>
int main()
{
int *ip=g_new(int,1);
*ip=42;
return *ip;
}
First I try apt-get libglib2.0-dev in my Ubuntu and Mint, when it's done, compile with:
gcc `pkg-config --cflags --libs glib-2.0` -o main main.c
/tmp/ccYFljQD.o: In function `main':
main.c:(.text+0x13): undefined reference to `g_malloc_n'
collect2: error: ld returned 1 exit status
Makefile:3: recipe for target 'all' failed
make: *** [all] Error 1
And the output of pkg-config:
$ pkg-config --cflags --libs glib-2.0
-I/usr/include/glib-2.0 -I/usr/lib/x86_64-linux-gnu/glib-2.0/include -lglib-2.0
So it's not working, then I try to compile from source and install one by my own.
I've apt-get libffi-dev, autogen and configure, make, make install, that's all okay.
$ pkg-config --cflags --libs glib-2.0
-I/home/donpope/software/include/glib-2.0 -I/home/donpope/software/lib/glib-2.0/include -L/home/donpope/software/lib -lglib-2.0
Yet compile with the same error:
gcc `pkg-config --cflags --libs glib-2.0` -o main main.c
/tmp/cctR3iEq.o: In function `main':
main.c:(.text+0x13): undefined reference to `g_malloc_n'
collect2: error: ld returned 1 exit status
Makefile:3: recipe for target 'all' failed
make: *** [all] Error 1
So I need some help here. Thank you!
Update:
Later I try this in a RedHat with older gcc. And it's just okay.

Answer 1

I have this Makefile in my glib sandbox:
PKGS=glib-2.0
CFLAGS+=$(shell pkg-config --cflags $(PKGS))
LDFLAGS+=$(shell pkg-config --libs $(PKGS))
%: %.c
$(CC) $(CFLAGS) $< -o $# $(LIBS) $(LDFLAGS)
%.o: %.c
$(CC) $(CFLAGS) $< -c -o $#
%: %.o
$(CC) $< -o $# $(LIBS) $(LDFLAGS)
Starting from this and tweaking, you should be able to figure out the exact commandline and compile your program.
Also, you should make sure that your PKG_CONFIG_PATH is properly updated to contain the path where you installed glib (typically in PREFIX/lib/pkgconfig).

Answer 2

Ubuntu 18.04 here. I had to place all my glib flags at the end of the compile statement, even after the source .c file. So this compiles fine:
gcc -Wall -o bfs bfs.c `pkg-config --cflags glib-2.0` `pkg-config --libs glib-2.0`
but this does not :
gcc -Wall -o bfs `pkg-config --cflags glib-2.0` `pkg-config --libs glib-2.0` bfs.c
/tmp/ccvWsLk3.o: In function `newGraph':
bfs.c:(.text+0x58): undefined reference to `g_hash_table_new'
collect2: error: ld returned 1 exit status
Which drove me nuts for a while as I was taught that it's always good style to place the source file at the end of the compile statement. :p