I'm new to ะก programming and have been trying to compile my code using MinGW/GCC, but I try to include cs50 (cs50.c, cs50.h) library, and the compiler can't find it. Help me compile who knows what's going on.
I tried to give such command: gcc -LC:\Users\apple\Desktop -lcs50 mario.c
But the result is this:
c:/mingw/bin/../lib/gcc/mingw32/8.2.0/../../../../mingw32/bin/ld.exe: cannot find -lcs50
collect2.exe: error: ld returned 1 exit status
Or:
c:/mingw/bin/../lib/gcc/mingw32/8.2.0/../../../../mingw32/bin/ld.exe: C:\Users\apple\AppData\Local\Temp\cc8KpeUr.o:mario.c:(.text+0x33): undefined reference to `GetInt'
collect2.exe: error: ld returned 1 exit status
This is my code:
#include <stdio.h>
#include <cs50.h>
int main()
{
int num = GetInt();
printf("%d\n",num);
}
gcc -LC:\Users\apple\Desktop -lcs50 mario.c
There are two problems here.
Always pass libraries after .c files or they won't actually do anything (unless main is in the library).
You appear to have a library called cs50.a; -lcs50 wants to find a file called libcs50.a or libcs50.so.
The easiest way around this problem is to not bother with -L or -l and just pass your library directly to gcc like this:
gcc mario.c cs50.a
Since cs50.c is a single file, you do not need a library at all. You can compile it as needed to save a few steps, it will consume a couple milliseconds more but most of the time you would not notice.
Just use
gcc mario.c cs50.c
and it will work (provided that both files are in the current folder).
I had the same problem. What i did was that i put the cs50.h and cs50.c files in the same folder or directory as stdio.h ; which you will find in the program files of the compiler you're using. It worked for me. Hope this helps.
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'm getting the following error and can't for the life of me figure out what I'm doing wrong.
$ gcc main.c -o main
Undefined symbols:
"_wtf", referenced from:
_main in ccu2Qr2V.o
ld: symbol(s) not found
collect2: ld returned 1 exit status
main.c:
#include <stdio.h>
#include "wtf.h"
main(){
wtf();
}
wtf.h:
void wtf();
wtf.c:
void wtf(){
printf("I never see the light of day.");
}
Now, if I include the entire function in the header file instead of just the signature, it complies fine so I know wtf.h is being included. Why doesn't the compiler see wtf.c? Or am I missing something?
Regards.
You need to link wtf with your main. Easiest way to compile it together - gcc will link 'em for you, like this:
gcc main.c wtf.c -o main
Longer way (separate compilation of wtf):
gcc -c wtf.c
gcc main.c wtf.o -o main
Even longer (separate compilation and linking)
gcc -c wtf.c
gcc -c main.c
gcc main.o wtf.o -o main
Instead of last gcc call you can run ld directly with the same effect.
You are missing the fact that merely including a header doesn't tell the compiler anything about where the actual implementation (the definitions) of the things declared in the header are.
They could be in a C file next to the one doing the include, they could come from a pre-compiled static link library, or a dynamic library loaded by the system linker when reading your executable, or they could come at run-time user programmer-controlled explicit dynamic loading (the dlopen() family of function in Linux, for instance).
C is not like Java, there is no implicit rule that just because a C file includes a certain header, the compiler should also do something to "magically" find the implementation of the things declared in the header. You need to tell it.
I need to call the following C code through R using GSL (GNU lib). The problem I'm having is in the compilation of the C code.
Here is the program mean.c:
#include <stdio.h>
#include <R.h>
#include <math.h>
#include <gsl/gsl_statistics.h>
void gsl(double *x, int *n)
{
double mean = gsl_stats_mean(x, 1, n);
Rprintf("mean = %f\n", mean);
}
Command> R CMD SHLIB mean.c
Output>
cygwin warning:
MS-DOS style path detected: C:/PROGRA~1/R/R-31~1.2/etc/i386/Makeconf
Preferred POSIX equivalent is: /cygdrive/c/PROGRA~1/R/R-31~1.2/etc/i386/Makeconf
CYGWIN environment variable option "nodosfilewarning" turns off this warning.
Consult the user's guide for more details about POSIX paths:
http://cygwin.com/cygwin-ug-net/using.html#using-pathnames
gcc -m32 -shared -s -static-libgcc -o mean.dll tmp.def mean.o ipconfig -Ld:/RCompile/CRANpkg/extralibs64/local/lib/i386 -Ld:/RCompile/CRANpkg/extralibs64/local/lib -LC:/PROGRA~1/R/R-31~1.2/bin/i386 -lR
mean.o:mean.c:<.text+0x1b>: undefined references to 'gsl_stats_mean'
collect2: ld returned 1 exit status
In the command Prompt I am giving the following command also:
>gcc mean.c -Wall -I"C:/Program Files/GnuWin32/include/gsl" -L"C:/Program Files/GnuWin32/lib" -lgslcblas -lgsl -lm -o mean
I have tried all the other permutations of putting mean.c in between and at the end but the compilation is terminated always, giving the message "ld returned 1 exit status". Sometimes giving the message 'R.h' - No such file or directory.
I have also edited the PATH and included GnuWin32 folder and its constituents.
Am I proceeding in the right direction?
Any help would be greatly appreciated, Thanks!
--Ankit
The RcppGSL package has working examples in the included and fully-working package as well as in a simpler spline example. In short, you need to supply a bit more to make and the compiler.
But as Martin Morgan noted in the comment, you also haven't exactly motivated why you would want to call the mean function from the GSL from R...
I want to compile a small program which has a pretty straight forward makefile, but I seem unable to get it working. Maybe you can help me. The makefile has the following targets:
visca-cli: visca-cli.c libvisca_hl.o
gcc -Wall -o visca-cli visca-cli.c /usr/local/lib/libvisca.so libvisca_hl.o
libvisca_hl.o: libvisca_hl.c
gcc -Wall -c libvisca_hl.c
I can 'make libvisca_hl.o' successfully and create the .o file. But 'make visca-cli' fails with error messages like
libvisca_hl.c:(.text+0x468a): undefined reference to
`VISCA_get_md_disptime'
for every single function defined in libvisca.h (here it's VISCA_get_md_disptime)
Here are the include sections from the various files (ommitting standard libraries):
In visca-cli.c:
#include "libvisca.h"
#include "libvisca_hl.h"
In libvisca_hl.c:
#include "libvisca_hl.h"
In libvisca_hl.h:
#include "libvisca.h"
All includes quoted with "" are present in the local directory where I run make and where all the sourcefiles are. There are no subfolders. So I guess the problem lies with the makefile? Any help appreciated!
The order of libraries and objects on your compilation/link command line matters. In your case, you just need to put the shared object at the end:
gcc -Wall -o visca-cli visca-cli.c libvisca_hl.o /usr/local/lib/libvisca.so
On most systems /usr/local/lib is already part of the standard library search path, so you could simplify further:
gcc -Wall -o visca-cli visca-cli.c libvisca_hl.o -lvisca
I'm getting the following error and can't for the life of me figure out what I'm doing wrong.
$ gcc main.c -o main
Undefined symbols:
"_wtf", referenced from:
_main in ccu2Qr2V.o
ld: symbol(s) not found
collect2: ld returned 1 exit status
main.c:
#include <stdio.h>
#include "wtf.h"
main(){
wtf();
}
wtf.h:
void wtf();
wtf.c:
void wtf(){
printf("I never see the light of day.");
}
Now, if I include the entire function in the header file instead of just the signature, it complies fine so I know wtf.h is being included. Why doesn't the compiler see wtf.c? Or am I missing something?
Regards.
You need to link wtf with your main. Easiest way to compile it together - gcc will link 'em for you, like this:
gcc main.c wtf.c -o main
Longer way (separate compilation of wtf):
gcc -c wtf.c
gcc main.c wtf.o -o main
Even longer (separate compilation and linking)
gcc -c wtf.c
gcc -c main.c
gcc main.o wtf.o -o main
Instead of last gcc call you can run ld directly with the same effect.
You are missing the fact that merely including a header doesn't tell the compiler anything about where the actual implementation (the definitions) of the things declared in the header are.
They could be in a C file next to the one doing the include, they could come from a pre-compiled static link library, or a dynamic library loaded by the system linker when reading your executable, or they could come at run-time user programmer-controlled explicit dynamic loading (the dlopen() family of function in Linux, for instance).
C is not like Java, there is no implicit rule that just because a C file includes a certain header, the compiler should also do something to "magically" find the implementation of the things declared in the header. You need to tell it.