I am trying to teach myself OpenMP using Windows 7, but I am having a hard time getting Code::Blocks to compile a basic hello world program:
#include <omp.h>
#include <stdio.h>
int main()
{
#pragma omp parallel
printf("Hello from thread %d, nthreads %d\n", omp_get_thread_num(), omp_get_num_threads());
}
I have made some progress, but there is one remaining persistent error that I can't get rid of.
I have -fopenmp in my compiler "Compiler->Compiler Settings->Other Options"
I have -gomp and -pthreads in "Compiler->Linker Settings->Other linker options"
I have C:\Program File (x86)\Codeblocks\MinGW\gcc\mingw32\bin in "Compiler->Toolchain exectuable->Additional Paths"
When I compile, I get the error: "ld.exe: cannot find -lpthread"
Can someone suggest what I might have set up wrong?
Thanks!
The linker complains about a missing library. pthreads is the library that implements the threading interface that your OpenMP implementation uses to do all the threading stuff.
The library is called "libpthread.a" (static version) and "libpthread.so" (dynamic version) on the disk. Try to find these two on the file system under your MinGW directory. They likely reside in a directory called "lib" or "lib64". If either one is missing, then you might need to install an additional package.
Cheers,
-michael
Related
I use Windows and codeblocks 13.12 IDE. I'm writing a C program need functions in <Winsock2.h> (like "WSAStartup" function) ; because Logs showed "Undefined Reference to WSAStartup", I included the command below according to the article WSAStartup link error.
#include <stdio.h>
#include <Winsock2.h>
#pragma comment(lib,"ws2_32.lib")
in case compiling process went wrong while linking library, I had put my program in a project and added "ws2_32.lib" into list of "Link libraries"; however, Logs only shows "cannot find -lws2_32.lib" I'm confused because I have checked that "ws2_32.dll" file exists in my C:\Windows\System32. How should I resolve the problem?
I'm trying to get a grasp on audio programming in C with OpenAL. I prefer CLion as an IDE to Visual Studio, but that generally means having to deal with cmake stuff and I ran into an issue regarding this. Right now I'm just trying to link the library (as in getting the definitions of the OpenAL functions) but it seems I've got something out of place. Here's the CMakeLists.txt file,
cmake_minimum_required(VERSION 3.19)
project(AudioTest C)
set(CMAKE_C_STANDARD 99)
set(OPENAL_LIBRARY "C:/Program Files (x86)/OpenAL 1.1 SDK/libs/Win64/") //OpenAL Installed here
find_package(OpenAL REQUIRED)
add_executable(AudioTest main.c)
target_link_libraries(AudioTest "${OPENAL_LIBRARY}")
The Cmake file compiles (or reloads) fine on it's own. But when I try to run this simple program,
#include <stdio.h>
#include <al.h>
int main() {
printf("Hello, World!\n");
alGetError();
return 0;
}
I end up with this,
undefined reference to '_imp__alGetError'
Could I get some pointers to what I might be missing?
I am on OS X 10.10 and trying to build a C 'project' with GLUT and OpenGL.
I reduced it to a minimal example showcasing my problem. I have the following CMakeLists.txt:
cmake_minimum_required(VERSION 2.8)
FIND_PACKAGE(OpenGL REQUIRED)
FIND_PACKAGE(GLUT REQUIRED)
if(OpenGL_FOUND) # never true, but printed as true
link_directories(${OpenGL_LIBRARY_DIRS})
include_directories(${OpenGL_INCLUDE_DIR})
endif(OpenGL_FOUND)
if(GLUT_FOUND)
link_directories(${GLUT_LIBRARY_DIR})
include_directories(${GLUT_INCLUDE_DIR})
endif(GLUT_FOUND)
# print all vars because wtf
get_cmake_property(_v VARIABLES)
foreach(_v ${_v})
message(STATUS "${_v}=${${_v}}")
endforeach()
add_executable(main main.c)
target_link_libraries(main ${GLUT_LIBRARY} ${OPENGL_LIBRARY})
The main.c is just a dummy including two headers:
#include <gl.h>
#include <glut.h>
int main()
{
return 0;
}
Now, cmake . runs fine and for debugging purposes prints all variables. I took the code from somewhere, I do not know enough about cmake to know whether it's doing what I think it is. Anyway, running make returns
main.c:1:10: fatal error: 'gl.h' file not found
#include <gl.h>
^
1 error generated.
The header gl.h is actually present in /System/Library/Frameworks/OpenGL.framework/Headers and as such should be found by cmake, especially since glut.h is in the same structure (simply replace OpenGL with GLUT) and is found just fine. Also, what is confusing to me is that the block in if(GLUT_FOUND)... is never executed (try to put a message statement into it), but among the printed variables it says OPENGL_FOUND=TRUE. But removing the if-condition does not change anything.
The actual question: What the hell is going on? Why does a) cmake not find the header unless specifically included, b) the if-block not execute although OPENGL_FOUND prints as TRUE, c) no such problems occur with glut.h? Spent hours on this and can't fathom why.
It's common to do
#if defined(__APPLE__)
#include <OpenGL/gl.h>
#include <OpenGL/glu.h>
#else
#include <GL/gl.h>
#include <GL/glu.h>
#endif
You can see this being done in one form or another in glfw, glew, sfml and others
I'm surprised that you found OpenGL headers in /System/Library/Frameworks in OS X 10.10. I don't think they have been installed there in quite a few Xcode releases. The most recent header files with Xcode 6.1 on 10.10 should be in:
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.10.sdk/System/Library/Frameworks/OpenGL.framework/Headers
You don't really need to know this path, unless you want to go look at the headers. I believe the compiler automatically uses the SDK that matches the OS you're compiling on. If for some reason you wanted to build for a different platform, you can override that logic with the -isysroot compiler option.
With header files that come from a framework, the naming you use in your #include statement is:
#include <FrameworkName/HeaderFileName.h>
The compiler will resolve this to the actual pathname of the header within the framework.
Therefore, if you want to use the current OpenGL header, which is gl3.h, from the OpenGL framework, the correct include statement is:
#include <OpenGL/gl3.h>
This will give you access to the Core Profile of the highest supported OpenGL version (which is 3.x or 4.x if you have a reasonably new Mac). Or if you want to use OpenGL 2.1 with legacy features:
#include <OpenGL/gl.h>
As pointed out bei pmr, CMake variables are case-sensitive, so the variable OPENGL_FOUND must be queried.
Also, as PeterT wrote, the header is included as #include <OpenGL/gl.h> on OS X.
I ended up coming to this question after updating qt installed from homebrew and had the same error messages. Going off of Reto's comment, I updated CMAKE_OSX_SYSROOT to /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk and everything went back to working as expected.
I have a newbie question about the C programming language. I have looked around to find the answer in similar questions but I failed to figure it out.
Assume a simple project consisting of two dirs: src and test. The source and header files are defined by src/main.c, test/foo.h and test/foo.c.
src/main.c:
#include "../test/foo.h"
int main (void) {
int a = VAR; /* works, recognizes declared macro */
some_function(a); /* doesn't work, "undefined reference" */
}
test/foo.h:
#ifndef FOO_H
#define FOO_H
void some_function(int a);
#define VAR 2;
#endif
test/foo.c (redundant but to be complete):
#include "foo.h"
#include <stdlib.h>
void some_function(int a) {
printf("%d", ++a);
}
I created the project in Eclipse and I also compile with it, I figured it wasn't a linking error since the macro gets recognized but the method is not callable.
The reason why I'm using different directories is because I have a lot of files and would like my test code to be separate from my main source code. Note that src and test have the same parent directory.
Any ideas what's going on here? Am I missing something very obvious?
Any help would be much appreciated, thanks in advance!
edit: I'm working on a (Debian) Linux machine and Eclipse uses the gcc compiler.
edit2: Thanks to H2CO3's answer I learned it is indeed a linking error. Since compiling and linking manually every time is quite an overhead, I was wondering if anyone knows how to teach Eclipse to link executables from different directories?
--------------------- SOLUTION ---------------------
edit3: Lol the solution was very easy after all, all I had to do was create a "new source folder" rather than a "new folder". I feel stupid but thanks to you all for replying, H2CO3 in particular!
I figured it wasn't a linking error since the macro gets recognized but the method is not callable.
Non sequitur. Macros are expanded in the preprocessing phase. (And as such, they have nothing to do with linkage at all.) You do have a linker error.
What you have to do is compile both files then link them together, so something like this should work:
gcc -Wall -o dir_one/foo.o dir_one/foo.c
gcc -Wall -o dir_two/bar.o dir_two/bar.c
gcc -o my_program dir_one/foo.o dir_two/bar.o
Also, read this SO question/answer and/or this article to understand how the steps of the compilation process work together. (These are almost the same for C and C++, it's only the name mangling that usually differs.)
Looking into learning C. As I understand it when I say #include <stdio.h> it grabs stdio.h from the default location...usually a directory inside your working directory called include. How do I actually get the file stdio.h? Do I need to download a bunch of .h files and move them from project to project inside the include directory? I did the following in a test.c file. I then ran make test and it outputted a binary. When I ran ./test I did not see hello print onto my screen. I thought I wasn't seeing output maybe because it doesn't find the stdio.h library. But then again if I remove the greater than or less than signs in stdio the compiler gives me an error. Any ideas?
I'm on a Mac running this from the command line. I am using: GNU Make 3.81. This program built for i386-apple-darwin10.0
#include <stdio.h>
main()
{
printf("hello");
}
Edit: I have updated my code to include a datatype for the main function and to return 0. I still get the same result...compiles without error and when I run the file ./test it doesn't print anything on screen.
#include <stdio.h>
int main()
{
printf("hello");
return 0;
}
Update:
If I add a \n inside of the printf it works! so this will work:
#include <stdio.h>
int main()
{
printf("hello\n");
return 0;
}
Your code should have preferably
printf("hello\n");
or
puts("hello");
If you want to know where does the standard header file <stdio.h> comes from, you could run your compiler with appropriate flags. If it is gcc, try compiling with
gcc -H -v -Wall hello.c -o hello
Pedantically, a standard header file is even not required to exist as a file; the standard permits an implementation which would process the #include <stdio.h> without accessing the file system (but e.g. by retrieving internal resources inside the compiler, or from a database...). Few compilers behave that way, most really access something in the file system.
If you didn't have the file, you'd get a compilation error.
My guess is the text was printed, but the console closed before you got the chance to see it.
Also, main returns an int, and you should return 0; to signal successful completion.
#include <header.h>, with angle brackets, searches in standard system locations, known to the compiler-- not in your project's subdirectories. In Unix systems (including your Mac, I believe), stdio.h is typically in /usr/include. If you use #include "header.h", you're searching subdirectories first and then the same places as with <header.h>.
But you don't need to find or copy the header to run your program. It is read at compilation time, so your ./test doesn't need it at all. Your program looks like it should have worked. Is it possible that you just typed "test", not "./test", and got the system command "test"? (Suggestion: Don't name your programs "test".)
Just going to leave this here : STILL! in 2018, December... Linux Mint 18.3
has no support for C development.
innocent / # cc ThoseSorts.c
ThoseSorts.c:1:19: fatal error: stdio.h: No such file or directory
compilation terminated.
innocent / # gcc ThoseSorts.c
ThoseSorts.c:1:19: fatal error: stdio.h: No such file or directory
compilation terminated.
innocent / # apt show libc6
(Abbreviated)::
Package: libc6
Version: 2.23-0ubuntu10
Priority: required
Section: libs
Source: glibc
Origin: Ubuntu
Installed-Size: 11.2 MB
Depends: libgcc1
Homepage: http://www.gnu.org/software/libc/libc.html
Description: GNU C Library: Shared libraries
Contains the standard libraries that are used by nearly all programs on
the system. This package includes shared versions of the standard C library
and the standard math library, as well as many others.
innocent / # apt-get install libc6-dev libc-dev
So, magic... and a minute later they are all installed on the
computer and then things work as they should.
Not all distros bundle up all the C support libs in each ISO.
Hunh.
hardlyinnocent / # gcc ThoseSorts.c
hardlyinnocent / # ./a.out
20
18
17
16
... ... ...