I'm new programming in C, now I'm trying to implement threads in a motor control program I am developing but my problem is that I can not run the pthread.h library in eclipse. despite haver installed POSIX threading library for Win32
Info: Internal Builder is used for build
gcc -O3 -g3 -Wall -pthread -c -fmessage-length=0 -o src\main.o ..\src\main.c
gcc: error: unrecognized option '-pthread'
Info: Parallel threads used: 1
Even though I'm just stating nothing but the library
#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
int main(void) {
return EXIT_SUCCESS;
}
check forum several times and did what they wanted to establish in the -pthread miscellaneous and link phtread but I can not solve the problem, could someone please help me?
I have Windows 10, 64 bits.
If your code is not compiling, you need to add -pthread argument in your gcc compilation as follows.
Navigate to: Project -> Properties
On the left: c/c++ build -> GCC C Compiler -> Miscellaneous
Add -pthread argument at the beginning Other Flags section
Also pthread library add c/c++ build -> Settings -> GCC C Linker -> Libraries
And include pthread library into other libraries.
Click apply.
Clean and build the project.
If you have only Unresolved inclusion problem alone then specify the file system path for the pthread.h as your compiler does not know this.
Check here how to add pthread.h in your filesystem.
I gave up trying, resort to the use of counters card that I use (KL25Z) and events programming.
Related
I have a C file, which uses multiple lib files.
I am trying to compile the file in the following way:
gcc -o myprogram main.c list.lib filelib.lib
However, when trying to compile I get a bunch of undefined reference errors of all the lib functions that I'm using.
I came accross a solution on the internet and tried the following:
gcc -o myprogram main.c -l list -l filelib
Now I get the following errors:
cannot find -llist
cannot fint -lfilelib
What am I doing wrong?
Edit:
Both the libs were originally created using Visual Studio 2019, Release mode x64.
I am using Windows 10, 64 bits architecture.
In the folder I'm running gcc from I have the following files:
main.c
list.lib (copied from VS)
list.h (copied form VS)
filelib.lib (copied from VS)
filelib.h (copied from VS)
In my lib code in VS I made sure the functions have c-linkage:
#ifdef __cplusplus
#define C_LINKAGE extern "C"
#else
#define C_LINKAGE
#endif
(each declared function in both the libs starts with the C_LINKAGE macro)
The .lib files are MSVC specific, gcc can not handle them, gcc can handle .a libraries or dll's (on windows)
If you want to use gcc, rebuild the libraries with gcc, or let MSVC create DLL's.
Or stick to microsoft and use MSVC for everything.
Just put "-l:liblist.lib" instead of "-llist" when the suffix is not ".a". That should solve the "Not found" issue at least.
I would like to give a BIG thanks to #Harkaitz for this hint.
I spent several days to figure out why GCC (arm cross compile on Windows) was not able to find my libs in group. I wish those spelling issues to be more documented somewhere...
Basically the ':' in between '-l' and 'lib.a' was solving the issue, like this:
-L./my_path_to_libs -Xlinker --start-group -l:libmain.a -Xlinker --end-group
Depending on arm gcc verzion, -Xlinker could be -Wl
I picked up the following demo off the web from https://computing.llnl.gov/tutorials/pthreads/
#include <pthread.h>
#include <stdio.h>
#define NUM_THREADS 5
void *PrintHello(void *threadid)
{
long tid;
tid = (long)threadid;
printf("Hello World! It's me, thread #%ld!\n", tid);
pthread_exit(NULL);
}
int main (int argc, char *argv[])
{
pthread_t threads[NUM_THREADS];
int rc;
long t;
for(t=0; t<NUM_THREADS; t++){
printf("In main: creating thread %ld\n", t);
rc = pthread_create(&threads[t], NULL, PrintHello, (void *)t);
if (rc){
printf("ERROR; return code from pthread_create() is %d\n", rc);
exit(-1);
}
}
pthread_exit(NULL);
}
But when I compile it on my machine (running Ubuntu Linux 9.04) I get the following error:
corey#ubuntu:~/demo$ gcc -o term term.c
term.c: In function ‘main’:
term.c:23: warning: incompatible implicit declaration of built-in function ‘exit’
/tmp/cc8BMzwx.o: In function `main':
term.c:(.text+0x82): undefined reference to `pthread_create'
collect2: ld returned 1 exit status
This doesn't make any sense to me, because the header includes pthread.h, which should have the pthread_create function. Any ideas what's going wrong?
For Linux the correct command is:
gcc -pthread -o term term.c
In general, libraries should follow sources and objects on command line, and -lpthread is not an "option", it's a library specification. On a system with only libpthread.a installed,
gcc -lpthread ...
will fail to link.
Read this or this detailed explanation.
For Linux the correct command is:
gcc -o term term.c -lpthread
you have to put -lpthread just after the compile command,this command will tell to the compiler to execute program with pthread.h library.
gcc -l links with a library file.Link -l with library name without the lib prefix.
in eclipse
properties->c/c++Build->setting->GCC C++ linker->libraries in top part add "pthread"
Running from the Linux terminal, what worked for me was compiling using the following command (suppose the c file I want to compile is called test.c):
gcc -o test test.c -pthread
Hope it helps somebody!
If you are using cmake, you can use:
add_compile_options(-pthread)
Or
SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -pthread")
I believe the proper way of adding pthread in CMake is with the following
find_package (Threads REQUIRED)
target_link_libraries(helloworld
${CMAKE_THREAD_LIBS_INIT}
)
Acutally, it gives several examples of compile commands used for pthreads codes are listed in the table below, if you continue reading the following tutorial:
https://computing.llnl.gov/tutorials/pthreads/#Compiling
Compile it like this : gcc demo.c -o demo -pthread
In Visual Studio 2019 specify -pthread in the property pages for the project under:
Linker -> Command Line -> Additional Options
Type in -pthread in the textbox.
You need to use the option -lpthread with gcc.
you need only Add "pthread" in proprieties=>C/C++ build=>GCC C++ Linker=>Libraries=> top part "Libraries(-l)".
thats it
check man page and you will get.
Compile and link with -pthread.
SYNOPSIS
#include <pthread.h>
int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
void *(*start_routine) (void *), void *arg);
Compile and link with -pthread.
....
Since none of the answers exactly covered my need (using MSVS Code), I add here my experience with this IDE and CMAKE build tools too.
Step 1: Make sure in your .cpp, (or .hpp if needed) you have included:
#include <functional>
Step 2 For MSVSCode IDE users:
Add this line to your c_cpp_properties.json file:
"compilerArgs": ["-pthread"],
Step 2 For CMAKE build tools users:
Add this line to your CMakeLists.txt
set(CMAKE_CXX_FLAGS "-pthread")
Note: Adding flag -lpthread (instead of -pthread) results in failed linking.
From man gcc,
-pthread
Define additional macros required for using the POSIX threads library.
You should use this option consistently for both compilation and linking.
This option is supported on GNU/Linux targets,
most other Unix derivatives,
and also on x86 Cygwin and MinGW targets.
It is correct that -pthread is an option and the best way to handle this.
There are statements in some answers that it generates different compiled code. This is misleading.
If you wish to duplicate -pthread, you could use -lpthread -D_REENTRANT=1. So there are two things going on with the -pthread option.
Indeed it links with the pthread library as many answers express. Also, the order of the pthread library is important because it may override some weak symbols. So a correct version using -lpthread may need to have it multiple times on the command line.
The other important part is the _REENTRANT define. Note, that this is in the implementation namespace. Some people may care for portability and other not. However, it is very important that it is defined as the first thing in the compilation unit. This symbol will alter the way that many system headers files are parsed.
You can include #define _REENTRANT 1 at the top of every source file, but it is much easier to have it on the command line. Again, the -pthread is the best way to achieve this. Also, gcc may change the way this is implemented in the future. However, I think it is important for programmers to understand what is going on.
term.c: In function ‘main’: term.c:23: warning: incompatible implicit
declaration of built-in function ‘exit’
You never included <stdlib.h>, where exit() is declared. Also, I think newer versions of gcc have removed the need for _REENTRANT.
Why features.h?
Example on godbolt, without -pthread.
So, it is NOT generating different code. Ie, the backend of the compiler is NOT different. It is only conditional compilation and linking to different libraries. It does not generate 'lock free' code or add appropriate machine barriers because you have used this option.
In Anjuta, go to the Build menu, then Configure Project.
In the Configure Options box, add:
LDFLAGS='-lpthread'
Hope it'll help somebody too...
Sometimes, if you use multiple library, check the library dependency.
(e.g. -lpthread -lSDL... <==> ... -lSDL -lpthread)
I am trying to build some Windows socket code using C. I've started with the following basic code to initialize WinSock:
#include <winsock2.h>
#include <stdio.h>
int main(int argc, char *argv[])
{
WSADATA wsa;
SOCKET s;
printf("\nInitialising Winsock...");
if (WSAStartup(MAKEWORD(2,2),&wsa) != 0)
{
printf("Failed. Error Code : %d",WSAGetLastError());
return 1;
}
printf("Initialised.\n");
};
When I run the code, I get errors such as:
undefined reference to '__imp_WSAStartup'
A quick google suggests this is to do with needing a library linking - ws2_32?
I was using Cygwin, but apparently this is trying to mimic a POSIX environment in Windows and hence MinGW is much more suited in this instance. Hence I've installed this and updated settings in VSCode to use it.
Now my problem is, I'm not sure how to link the required library. Do I do it within my program by adding some code? Do I do it in some sort of separate terminal?
This is all new to me.
Using Cygwin as an environment to code is not recommenced. (See pros and cons of using Cygwin.) Pick one environment or the other. i.e. run GCC in either Windows or Linux, but not both. Code::Blocks comes bundled with GCC, and has versions that can be used in either Windows or Linux.
And yes, the error message undefined reference to indicates that although the header file is there, the library it refers to is not. It needs to be linked using Ws2_32.lib.
If using the Code::Blocks IDE for example, the instruction for linking a library are here.
Or, from the command line using GCC:
For example, if I have a library named libmine.so in
/home/newhall/lib/ then I'd do the following to link it into my
program:
$ gcc -o myprog myprog.c -L/home/newhall/lib -lmine //Linux
C:\> gcc -o myprog myprog.c -LC:\home\newhall\lib -lmine //Windows
...more on gcc command line here.
The line that links your code to a .exe file needs to include -lws2_32 after the .o or .c file.
So in your case if your program is called myprogram.c you would need to run:
gcc -o myprogram.exe myprogram.c -lws2_32
or if you compile and link in seperate steps:
gcc -c -o myprogram.o myprogram.c
gcc -o myprogram.exe myprogram.o -lws2_32
I have tried to compile a C program using FFMPEG but every time I compile it fails at the include statement:
#include <libavcodec/avcodec.h>
#include <libavformat/avformat.h>
Gcc provides this error message:
libavcodec/avcodec.h: No such file or directory
I have installed FFMPEG and created the shared libraries, but when I try to link those libraries when I compile I get the same error.
gcc main.c -L ffmpeg_build/lib -l ffmpeg_build/include/libavcodec/avcodec.h
Do I get this error because I am linking the library incorrectly, or is there some other issue?
This is the first time I am using someone else's library, so please excuse me if I am asking a silly question.
A lowercase -l is a linker option used to specify libraries. They might look like libsomething.a and becomes -lsomething in the linker invocation. In order to add a directory to the header search path, use a capital i, -I.
gcc main.c -L/some/path/ffmpeg_build/lib -I/some/path/ffmpeg_build/include
I picked up the following demo off the web from https://computing.llnl.gov/tutorials/pthreads/
#include <pthread.h>
#include <stdio.h>
#define NUM_THREADS 5
void *PrintHello(void *threadid)
{
long tid;
tid = (long)threadid;
printf("Hello World! It's me, thread #%ld!\n", tid);
pthread_exit(NULL);
}
int main (int argc, char *argv[])
{
pthread_t threads[NUM_THREADS];
int rc;
long t;
for(t=0; t<NUM_THREADS; t++){
printf("In main: creating thread %ld\n", t);
rc = pthread_create(&threads[t], NULL, PrintHello, (void *)t);
if (rc){
printf("ERROR; return code from pthread_create() is %d\n", rc);
exit(-1);
}
}
pthread_exit(NULL);
}
But when I compile it on my machine (running Ubuntu Linux 9.04) I get the following error:
corey#ubuntu:~/demo$ gcc -o term term.c
term.c: In function ‘main’:
term.c:23: warning: incompatible implicit declaration of built-in function ‘exit’
/tmp/cc8BMzwx.o: In function `main':
term.c:(.text+0x82): undefined reference to `pthread_create'
collect2: ld returned 1 exit status
This doesn't make any sense to me, because the header includes pthread.h, which should have the pthread_create function. Any ideas what's going wrong?
For Linux the correct command is:
gcc -pthread -o term term.c
In general, libraries should follow sources and objects on command line, and -lpthread is not an "option", it's a library specification. On a system with only libpthread.a installed,
gcc -lpthread ...
will fail to link.
Read this or this detailed explanation.
For Linux the correct command is:
gcc -o term term.c -lpthread
you have to put -lpthread just after the compile command,this command will tell to the compiler to execute program with pthread.h library.
gcc -l links with a library file.Link -l with library name without the lib prefix.
in eclipse
properties->c/c++Build->setting->GCC C++ linker->libraries in top part add "pthread"
Running from the Linux terminal, what worked for me was compiling using the following command (suppose the c file I want to compile is called test.c):
gcc -o test test.c -pthread
Hope it helps somebody!
If you are using cmake, you can use:
add_compile_options(-pthread)
Or
SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -pthread")
I believe the proper way of adding pthread in CMake is with the following
find_package (Threads REQUIRED)
target_link_libraries(helloworld
${CMAKE_THREAD_LIBS_INIT}
)
Acutally, it gives several examples of compile commands used for pthreads codes are listed in the table below, if you continue reading the following tutorial:
https://computing.llnl.gov/tutorials/pthreads/#Compiling
Compile it like this : gcc demo.c -o demo -pthread
In Visual Studio 2019 specify -pthread in the property pages for the project under:
Linker -> Command Line -> Additional Options
Type in -pthread in the textbox.
You need to use the option -lpthread with gcc.
you need only Add "pthread" in proprieties=>C/C++ build=>GCC C++ Linker=>Libraries=> top part "Libraries(-l)".
thats it
check man page and you will get.
Compile and link with -pthread.
SYNOPSIS
#include <pthread.h>
int pthread_create(pthread_t *thread, const pthread_attr_t *attr,
void *(*start_routine) (void *), void *arg);
Compile and link with -pthread.
....
Since none of the answers exactly covered my need (using MSVS Code), I add here my experience with this IDE and CMAKE build tools too.
Step 1: Make sure in your .cpp, (or .hpp if needed) you have included:
#include <functional>
Step 2 For MSVSCode IDE users:
Add this line to your c_cpp_properties.json file:
"compilerArgs": ["-pthread"],
Step 2 For CMAKE build tools users:
Add this line to your CMakeLists.txt
set(CMAKE_CXX_FLAGS "-pthread")
Note: Adding flag -lpthread (instead of -pthread) results in failed linking.
From man gcc,
-pthread
Define additional macros required for using the POSIX threads library.
You should use this option consistently for both compilation and linking.
This option is supported on GNU/Linux targets,
most other Unix derivatives,
and also on x86 Cygwin and MinGW targets.
It is correct that -pthread is an option and the best way to handle this.
There are statements in some answers that it generates different compiled code. This is misleading.
If you wish to duplicate -pthread, you could use -lpthread -D_REENTRANT=1. So there are two things going on with the -pthread option.
Indeed it links with the pthread library as many answers express. Also, the order of the pthread library is important because it may override some weak symbols. So a correct version using -lpthread may need to have it multiple times on the command line.
The other important part is the _REENTRANT define. Note, that this is in the implementation namespace. Some people may care for portability and other not. However, it is very important that it is defined as the first thing in the compilation unit. This symbol will alter the way that many system headers files are parsed.
You can include #define _REENTRANT 1 at the top of every source file, but it is much easier to have it on the command line. Again, the -pthread is the best way to achieve this. Also, gcc may change the way this is implemented in the future. However, I think it is important for programmers to understand what is going on.
term.c: In function ‘main’: term.c:23: warning: incompatible implicit
declaration of built-in function ‘exit’
You never included <stdlib.h>, where exit() is declared. Also, I think newer versions of gcc have removed the need for _REENTRANT.
Why features.h?
Example on godbolt, without -pthread.
So, it is NOT generating different code. Ie, the backend of the compiler is NOT different. It is only conditional compilation and linking to different libraries. It does not generate 'lock free' code or add appropriate machine barriers because you have used this option.
In Anjuta, go to the Build menu, then Configure Project.
In the Configure Options box, add:
LDFLAGS='-lpthread'
Hope it'll help somebody too...
Sometimes, if you use multiple library, check the library dependency.
(e.g. -lpthread -lSDL... <==> ... -lSDL -lpthread)