I am trying to compile the code:
#include <stdio.h>
#include <omp.h>
int main(){
#pragma omp parallel
{
printf("%d\t%d\n",omp_get_thread_num(), omp_get_num_threads());
}
return 0;
}
I tried both cc -o main.exe main.c and gcc -o main.exe main.c
Both ways I get "fatal error: 'omp.h' file not found"
So I downloaded the latest version of OpenMP. Then in the terminal in the directory of the downloaded folder I typed make and then
sudo cp ./libiomp5.dylib /usr/lib/
but I am still having the same issue. How can I get this to compile?
You should guard the Openmp include and function calls with #if _OPENMP in order to support compiling without the openmp option (gcc -fopenmp).
Related
For this question of mine, my goal was to create a software, main, that takes a plugin, libfunc.so, and libfunc.so would modify the value of burger.
main.c :
#include <stdio.h>
#include <stdlib.h> // for exit()
#include <dlfcn.h>
#include "main.h"
int burger = 3;
int main(){
void (*ptr_func)();
void *handle;
handle = dlopen("./libfunc.so", RTLD_NOW);
if (!handle) {
fprintf(stderr, "%s\n", dlerror());
exit(1);
}
*(void**)(&ptr_func) = dlsym(handle, "some_func");
if (!ptr_func){
fprintf(stderr, "%s\n", dlerror());
dlclose(handle);
exit(1);
}
printf("before ptr_func %d\n", burger);
ptr_func();
printf("after %d\n", burger);
return 0;
}
The declaration of burger,
main.h:
#ifndef MAIN_H__
#define MAIN_H__
extern int burger;
#endif
and the plugin [func.c] as this:
#include <stdio.h>
#include "main.h"
void some_func(){
burger += 10;
}
compiled all of these with clang and I got no error:
$ clang -rdynamic main.c -o main
$ clang -shared -fPIC func.c -o libfunc.so
But the problem arises with gcc:
$ gcc -rdynamic main.c -o main
$ gcc -shared -fPIC func.c -o libfunc.so
/usr/lib/gcc/x86_64-pc-cygwin/9.3.0/../../../../x86_64-pc-cygwin/bin/ld: /tmp/cc
vgKpEc.o:func.c:(.rdata$.refptr.burger[.refptr.burger]+0x0): undefined reference
to `burger'
Yes, I've tried removing the extern and it compiled successfully but the output was:
$ ./main.exe
before ptr_func 3
after 3
clang on the other hand compiled this successfully and working as I expected:
$ ./main
before ptr_func 3
after 13
The same as without extern compiled in clang
Do this two rivals really don't like to be consistent?
Here's the gist of it https://gist.github.com/harieamjari/8c816f39fe04d38d83022301872272ea
Additional notes:
The clang I have was from Termux. (an android application that simulates linux).
And the gcc I have was from cygwin.
gcc version 9.3.0
clang version 9.0.0
NOTICE
From my Termux, I installed gnu-8 and compiled the MWE above, but I do not experience an error.
Maybe I should use Windows.h for this matter instead of using dlfcn.h in cygwin.
I have source files written in C programming using notepad++ and I am running them from command lines and later i need to link them inorder to generate the .exe file.
Here are the following commands I want to use while generating .exe file
gcc logc.c -o logc
gcc mainc.c -o mainc
gcc -o output logc.o mainc.o
But when i run the following command my compiler is returning with the following error status.
gcc logc.c -o logc
(x86)/mingw-w64/i686-8.1.0-win32-dwarf-rt_v6-rev0/mingw32/bin/../lib/gcc/i686-w64-mingw32/8.1.0/../../../../i686-w64-mingw32/lib/../lib/libmingw32.a(lib32_libmingw32_a-crt0_c.o):crt0_c.c:(.text.startup+0x39): undefined reference to `WinMain#16'
when i run the following command to compile my mainc file
C:\Users\user\AppData\Local\Temp\ccskY3nf.o:mainc.c:(.text+0x31): undefined reference to `Log'
collect2.exe: error: ld returned 1 exit status
And here are my mainc.c and logc.c and logc.h files for your reference
logc.c file is here
#include <stdio.h>
#include "logc.h"
void InitLog()
{
Log("Initializing Log");
}
void Log(const char* message)
{
printf(" %s",message);
}
mainc.c file is here
#include <stdio.h>
#include <conio.h>
#include <stdbool.h>
#include "logc.h"
int main()
{
int x = 5;
bool comparisonResult = x == 5;
if(comparisonResult == 1)
Log("Hello World");
return 0;
}
and logc.h file is here
#ifndef _LOG_H
#define _LOG_H
void InitLog();
void Log(const char* message);
#endif
How can i compile individual source files and then link them and generate an executable file.
Thanks in advance.
You don't create object files, for that you need the -c argument:
gcc logc.c -c
gcc mainc.c -c
gcc -o output logc.o mainc.o
By default gcc will generate an executable file, not an object file. So when you compile logc.c, it tries to make an executable but it can't find the main function so it fails. Similarly with main.c, it tries to make an executable but can't find Log
You need to add the -c option to create object files:
gcc logc.c -c -o logc.o
gcc mainc.c -c -o mainc.o
I'm pretty sure this is a simple question but I've searched online for about half an hour.
I have 3 files:
02_01.c
#include <stdio.h> // Notice the library included in the header of this file
#include <stdlib.h>
#include "myLibrary.h" // Notice that myLibrary.h uses different include syntax
#define MAX_LENGTH 21.8
#define WORK_WEEK 5
int main(void) {
function1();
return EXIT_SUCCESS;
}
myLibrary.c
void function1(void){
puts("It works :)");
}
void function2(void){
//This function does nothing as well
}
myLibrary.h
#ifndef MYLIBRARY_H_
#define MYLIBRARY_H_
void function1(void);
void function2(void);
#endif /* MYLIBRARY_H_ */
First, I navigate to my working directory.
Normally in a file with no local headers I would type:
gcc -o 02_01 02_01.c
./02_01
and it would work.
I've tried a variety of things like:
gcc -o 02_01 02_01.c myLibrary.c
which gives me an error "implicit declaration of function 'puts'
gcc -o myLibrary myLibrary.c which also gives the same error.
What should I be typing in the terminal in ubuntu?
So I'm assuming that the puts() function in myLibrary.c is not connected to 02_01.c which is where I include stdio.h.
You must include required headers in every file, where you using included functions. In your case, you must include #include <stdio.h> in beginning of your myLibrary.c file.
Also, you probably want to build .a library and link with it later.
So, finally:
Compile lib:
gcc -c -o mylib myLibrary.c
Make static lib:
ar rcs libMyLib.a mylib
Compile app and link together:
gcc -o 02_01 02_01.c -L. -lMyLib
I have a c script
#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <time.h>
#include <gsl/gsl_rng.h>
#include <gsl/gsl_randist.h>
int main(void)
{
const gsl_rng_type * T;
gsl_rng * r;
int i;
double a,b;
double num;
a=10;
b=7.2;
gsl_rng_env_setup();
T=gsl_rng_default;
r=gsl_rng_alloc (T);
for(i=0; i<10; i++)
{
num = gsl_ran_gamma(r,a,b);
printf("%.8f \n",num);
}
gsl_rng_free(r);
return 0;
}
Which I have successfully compiled on a linux machine. I want to use the gsl library for other applications on my mac. So I first installed gsl using homebrew which seemed to be successful. To make sure everything was working right I tried to compile and run this script as follows
[ACC-259-imac:GDSC Gene Expression Modeling jmannhei$ gcc -Wall gamma.c -o gamma.out -lm -lgsl -lgslcblas
which resulted in the following output
gamma.c:5:10: fatal error: 'gsl/gsl_rng.h' file not found
#include <gsl/gsl_rng.h>
^
1 error generated.
Which is exactly how I compiled it on Linux so I am not sure what is awry as I have compile c scripts in the past using this format from terminal on a mac before. My guess is it is not linking properly but I am not sure what I need to do to fix it. Thanks
Find your header file directory with brew list gsl or locate gsl/gsl_rng.h then tell your compiler where the headers are. I would need the following, for example,
gcc -Wall -I/usr/local/Cellar/gsl/1.16/include/ gamma.c -o gamma.out -lm -lgsl -lgslcblas
I have these five source
main.c src_print1.c src_print2.c header_print1.h header_print2.h
the contents are simple and are as following for respective files:
main.c
#include "header_print1.h"
#include "header_print2.h"
int main(int argc, char** argv) {
print1();
print2();
return 0;
}
header_print1.h
#ifndef PRINT_1
#define PRINT_1
#include <stdio.h>
#include <stdlib.h>
void print1();
#endif
header_print2.h
#ifndef PRINT_2
#define PRINT_2
#include <stdio.h>
#include <stdlib.h>
void print2();
#endif
src_print1.c
#include "header_print1.h"
void print1() {
printf("Hello 1\n");
}
src_print2.c
#include "header_print2.h"
void print2() {
printf("Hello 2\n");
}
Using gcc I have tried to compile using the following command line:
gcc -I ./ -o test -c main.c src_print1.c src_print2.c
Everything is in the same folder.
The error I get is:
gcc: cannot specify -o with -c or -S with multiple files
I looked up at gcc manual, but actually I don't understand what to do in this case, since usually I use IDE and not the command line.
IMHO, if you rewrite your compilation statement like
gcc -I./ -o test main.c src_print1.c src_print2.c
You'll be good to go. There is no need for -c flag [NOTE] when you're specifying the output binary using -o.
Also, as mentioned here, all the files are in same directory, you can even shorten the statement as
gcc -o test main.c src_print1.c src_print2.c
Suggestion: While the above change(s) will do the job, this is not considered an elegant way of doing so. Please consider creating a makefile which will make your life easier.
[Note]:
Regarding the -c option, as per the online gcc manual, (emphasis mine)
-c
Compile or assemble the source files, but do not link. The linking stage simply is not done. The ultimate output is in the form of an object file for each source file.
So, it should be clear by now, why you got the error.