I´m trying to produce a little example code for the library libfixmath and I get the error "undefined reference to `fix16_mul' "
The code is:
#include <stdio.h>
#include "libfixmath/fixmath.h"
int main(){
fix16_t res = fix16_mul(fix16_from_int(1), fix16_from_int(2));
return 0;
}
The library is at the specified path and I compile just with the command
gcc -o testfix testfix.c
The documentation says
To use the fixmath library, include the header <fixmath/fixmath.h>, and link the application with -lfixmath, or use pkg-config to determine the compiler and linker flags.
So change
gcc -o testfix testfix.c
to
gcc -o testfix testfix.c -lfixmath
and it should work.
Related
I have this simple code:
max = (int) sqrt (number);
and in the header I have:
#include <math.h>
But application still says undefined reference to sqrt. Do you see any problem here? It looks like everything should be okay.
You may find that you have to link with the math libraries on whatever system you're using, something like:
gcc -o myprog myprog.c -L/path/to/libs -lm
^^^ - this bit here.
Including headers lets a compiler know about function declarations but it does not necessarily automatically link to the code required to perform that function.
Failing that, you'll need to show us your code, your compile command and the platform you're running on (operating system, compiler, etc).
The following code compiles and links fine:
#include <math.h>
int main (void) {
int max = sqrt (9);
return 0;
}
Just be aware that some compilation systems depend on the order in which libraries are given on the command line. By that, I mean they may process the libraries in sequence and only use them to satisfy unresolved symbols at that point in the sequence.
So, for example, given the commands:
gcc -o plugh plugh.o -lxyzzy
gcc -o plugh -lxyzzy plugh.o
and plugh.o requires something from the xyzzy library, the second may not work as you expect. At the point where you list the library, there are no unresolved symbols to satisfy.
And when the unresolved symbols from plugh.o do appear, it's too late.
I suppose you have imported math.h with #include <math.h>
So the only other reason I can see is a missing linking information. You must link your code with the -lm option.
If you're simply trying to compile one file with gcc, just add -lm to your command line, otherwise, give some informations about your building process.
Just adding the #include <math.h> in c source file and -lm in Makefile at the end will work for me.
gcc -pthread -o p3 p3.c -lm
Here are my observation, firstly you need to include the header math.h as sqrt() function declared in math.h header file. For e.g
#include <math.h>
secondly, if you read manual page of sqrt you will notice this line Link with -lm.
#include <math.h> /* header file you need to include */
double sqrt(double x); /* prototype of sqrt() function */
Link with -lm. /* Library linking instruction */
But application still says undefined reference to sqrt. Do you see any
problem here?
Compiler error is correct as you haven't linked your program with library lm & linker is unable to find reference of sqrt(), you need to link it explicitly. For e.g
gcc -Wall -Wextra -Werror -pedantic test.c -lm
I had the same issue, but I simply solved it by adding -lm after the command that runs my code.
Example.
gcc code.c -lm
I have this simple code:
max = (int) sqrt (number);
and in the header I have:
#include <math.h>
But application still says undefined reference to sqrt. Do you see any problem here? It looks like everything should be okay.
You may find that you have to link with the math libraries on whatever system you're using, something like:
gcc -o myprog myprog.c -L/path/to/libs -lm
^^^ - this bit here.
Including headers lets a compiler know about function declarations but it does not necessarily automatically link to the code required to perform that function.
Failing that, you'll need to show us your code, your compile command and the platform you're running on (operating system, compiler, etc).
The following code compiles and links fine:
#include <math.h>
int main (void) {
int max = sqrt (9);
return 0;
}
Just be aware that some compilation systems depend on the order in which libraries are given on the command line. By that, I mean they may process the libraries in sequence and only use them to satisfy unresolved symbols at that point in the sequence.
So, for example, given the commands:
gcc -o plugh plugh.o -lxyzzy
gcc -o plugh -lxyzzy plugh.o
and plugh.o requires something from the xyzzy library, the second may not work as you expect. At the point where you list the library, there are no unresolved symbols to satisfy.
And when the unresolved symbols from plugh.o do appear, it's too late.
I suppose you have imported math.h with #include <math.h>
So the only other reason I can see is a missing linking information. You must link your code with the -lm option.
If you're simply trying to compile one file with gcc, just add -lm to your command line, otherwise, give some informations about your building process.
Just adding the #include <math.h> in c source file and -lm in Makefile at the end will work for me.
gcc -pthread -o p3 p3.c -lm
Here are my observation, firstly you need to include the header math.h as sqrt() function declared in math.h header file. For e.g
#include <math.h>
secondly, if you read manual page of sqrt you will notice this line Link with -lm.
#include <math.h> /* header file you need to include */
double sqrt(double x); /* prototype of sqrt() function */
Link with -lm. /* Library linking instruction */
But application still says undefined reference to sqrt. Do you see any
problem here?
Compiler error is correct as you haven't linked your program with library lm & linker is unable to find reference of sqrt(), you need to link it explicitly. For e.g
gcc -Wall -Wextra -Werror -pedantic test.c -lm
I had the same issue, but I simply solved it by adding -lm after the command that runs my code.
Example.
gcc code.c -lm
I have some problems compiling my test program using PDCurses library. I have compiled PDCurses 3.4 with MinGW compiler 8.2.0. In output I have 2 files panel.a and pdcurses.a. I copied them to C:\MinGW\lib plus the header file curses.h in C:\MinGW\include. But when I try to compile test program I have errors. It seems I have done everything correctly according to instructions and how-to`s.
Some testing C code:
#include <C:\MinGW\include\curses.h>
int main () {
initscr();
mvprintw( 5, 5, "Hello, World!" );
getch();
endwin();
return 0;
}
ERRORS:
c:/Users/username/Dropbox/rakshasa/main.c:4: undefined reference to `initscr'
c:/mingw/bin/../lib/gcc/mingw32/8.2.0/../../../../mingw32/bin/ld.exe: c:/Users/username/Dropbox/rakshasa/main.c:5: undefined reference to `mvprintw'
c:/mingw/bin/../lib/gcc/mingw32/8.2.0/../../../../mingw32/bin/ld.exe: c:/Users/username/Dropbox/rakshasa/main.c:6: undefined reference to `stdscr'
c:/mingw/bin/../lib/gcc/mingw32/8.2.0/../../../../mingw32/bin/ld.exe: c:/Users/username/Dropbox/rakshasa/main.c:6: undefined reference to `wgetch'
c:/mingw/bin/../lib/gcc/mingw32/8.2.0/../../../../mingw32/bin/ld.exe: c:/Users/username/Dropbox/rakshasa/main.c:7: undefined reference to `endwin'
I have no idea why it is not compiling properly. It looks like compiler cant find libraries in linking stage but I do not know why.
I was try to compile like
gcc -g main.c -o main.exe
Thanks in advance.
Never use absolute paths in #include directives. Instead of #include <C:\MinGW\include\curses.h> you should put #include <curses.h> and compile with -IC:\MinGW\include flag if needed.
Next you need to link with the relevant library using -lpdcurses. If needed you can add the location of the library using -LC:\MinGW\lib.
So if we split compilation and linking steps you need the following commands:
gcc -g main.c -c -o main.o -IC:\MinGW\include
gcc main.o -o main.exe -lpdcurses -LC:\MinGW\lib
though I think you can leave out the -I and -L flags as they point to the location of your compiler's include and lib folders.
Finally: MinGW is a bit outdated and so is GCC 8.2.0. I recommend you switch to MinGW-w64 (which supports both 32-bit and 64-bit Windows). To get a more recent MinGW-w64 GCC build, you can try the standalone builds from https://winlibs.com/.
I have this simple code:
max = (int) sqrt (number);
and in the header I have:
#include <math.h>
But application still says undefined reference to sqrt. Do you see any problem here? It looks like everything should be okay.
You may find that you have to link with the math libraries on whatever system you're using, something like:
gcc -o myprog myprog.c -L/path/to/libs -lm
^^^ - this bit here.
Including headers lets a compiler know about function declarations but it does not necessarily automatically link to the code required to perform that function.
Failing that, you'll need to show us your code, your compile command and the platform you're running on (operating system, compiler, etc).
The following code compiles and links fine:
#include <math.h>
int main (void) {
int max = sqrt (9);
return 0;
}
Just be aware that some compilation systems depend on the order in which libraries are given on the command line. By that, I mean they may process the libraries in sequence and only use them to satisfy unresolved symbols at that point in the sequence.
So, for example, given the commands:
gcc -o plugh plugh.o -lxyzzy
gcc -o plugh -lxyzzy plugh.o
and plugh.o requires something from the xyzzy library, the second may not work as you expect. At the point where you list the library, there are no unresolved symbols to satisfy.
And when the unresolved symbols from plugh.o do appear, it's too late.
I suppose you have imported math.h with #include <math.h>
So the only other reason I can see is a missing linking information. You must link your code with the -lm option.
If you're simply trying to compile one file with gcc, just add -lm to your command line, otherwise, give some informations about your building process.
Just adding the #include <math.h> in c source file and -lm in Makefile at the end will work for me.
gcc -pthread -o p3 p3.c -lm
Here are my observation, firstly you need to include the header math.h as sqrt() function declared in math.h header file. For e.g
#include <math.h>
secondly, if you read manual page of sqrt you will notice this line Link with -lm.
#include <math.h> /* header file you need to include */
double sqrt(double x); /* prototype of sqrt() function */
Link with -lm. /* Library linking instruction */
But application still says undefined reference to sqrt. Do you see any
problem here?
Compiler error is correct as you haven't linked your program with library lm & linker is unable to find reference of sqrt(), you need to link it explicitly. For e.g
gcc -Wall -Wextra -Werror -pedantic test.c -lm
I had the same issue, but I simply solved it by adding -lm after the command that runs my code.
Example.
gcc code.c -lm
Trying to get getch() working to capture key press.
#include <curses.h>
...
...
WINDOW *w;
char f;
w = initscr();
timeout(3000);
f = getch();
endwin();
is giving me following error:-
undefined reference to `wgetch'
undefined reference to `stdscr'
That's a linking error. Are you linking to the curses library correctly?
There are two steps involved in using a library in C.
You #include the relevant header files from your source files. This is so your code knows what signatures of the library functions are. So you're doing this correctly.
When compiling your code, you need to tell the linker to link to the relevant libraries, so it can find the definition of those functions. This is what you're not doing. Assuming you're using gcc then adding -lncurses to the compile line should do it. Here's an explanation of linking.
The above answers are correct but the format is:
gcc -Wall program.c -o name_of_binary -lncurses
When I did:
gcc -Wall -lncurses program.c...
It did not work so apparently it should be tacked on the end.