I just started learning C, and wrote my hello world program:
#include <stdio.h>
main()
{
printf("Hello World");
return 0;
}
When I run the code, I get a really long error:
Apple Mach-O Linker (id) Error
Ld /Users/Solomon/Library/Developer/Xcode/DerivedData/CProj-cwosspupvengheeaapmkrhxbxjvk/Build/Products/Debug/CProj normal x86_64
cd /Users/Solomon/Desktop/C/CProj
setenv MACOSX_DEPLOYMENT_TARGET 10.7
/Developer/usr/bin/clang -arch x86_64 -isysroot /Developer/SDKs/MacOSX10.7.sdk -L/Users/Solomon/Library/Developer/Xcode/DerivedData/CProj-cwosspupvengheeaapmkrhxbxjvk/Build/Products/Debug -F/Users/Solomon/Library/Developer/Xcode/DerivedData/CProj-cwosspupvengheeaapmkrhxbxjvk/Build/Products/Debug -filelist /Users/Solomon/Library/Developer/Xcode/DerivedData/CProj-cwosspupvengheeaapmkrhxbxjvk/Build/Intermediates/CProj.build/Debug/CProj.build/Objects-normal/x86_64/CProj.LinkFileList -mmacosx-version-min=10.7 -o /Users/Solomon/Library/Developer/Xcode/DerivedData/CProj-cwosspupvengheeaapmkrhxbxjvk/Build/Products/Debug/CProj
ld: duplicate symbol _main in /Users/Solomon/Library/Developer/Xcode/DerivedData/CProj-cwosspupvengheeaapmkrhxbxjvk/Build/Intermediates/CProj.build/Debug/CProj.build/Objects-normal/x86_64/helloworld.o and /Users/Solomon/Library/Developer/Xcode/DerivedData/CProj-cwosspupvengheeaapmkrhxbxjvk/Build/Intermediates/CProj.build/Debug/CProj.build/Objects-normal/x86_64/main.o for architecture x86_64
Command /Developer/usr/bin/clang failed with exit code 1
I am running xCode
Should I reinstall DevTools?
If you read the error messages (specifically the line starting ld: duplicate symbol _main in ...), you'll notice that it's complaining about two main functions, one in:
......blah blah blah/helloworld.o
and the other in:
......yada yada yada/main.o
That means your project is screwed up somehow. Either you have two separate source files containing main or Xcode is supplying one automagically.
You just need to fix that.
Here's how to interpret that message:
Apple Mach-O Linker (id) Error
An error occurred
Ld /Users/ …
cd …
setenv …
/Developer/…
This is the command that Xcode executed to perform the linking step. You can almost always ignore it and skip past the next blank line.
ld: duplicate symbol _main in /Users/…/helloworld.o and /Users/…/main.o for architecture x86_64
This is the actual error message. It tells you that you have duplicate _main symbols, one in the file helloworld.o and one in main.o. This means you have to functions which are both called main, which isn't allowed. One of them is in helloworld.c and the other is in main.c. If you delete one of these functions or files, the error will go away.
Command /Developer/usr/bin/clang failed with exit code 1
This tells you the exit code of the command Xcode performed. It is less helpful than the error message, and I have never seen anything other than 1 for linking errors.
I meet this problem as well. In "Target Membership", just tick the file you want to run. Untick this in other files you don't want to run. Then try again.
It is also important to remember that you could have received this error message if you had a #include "...filename..." that created a duplicate copy of your function calls. However, in your case, that is not likely.
remember that #include essentially just copies and pastes a copy of your code where the #include takes place.
Related
So I am trying to compile ,link and run a program without the main function.This is the code:
#include <stdio.h>
#include <stdlib.h>
int my_main()
{
printf("Hello world!\n");
return 0;
}
void _start()
{
exit(my_main());
}
Tried to compile with the command : gcc -nostartfiles nomain.c . While it does compile and produces the a.out file on a Debian vm, I am unable to compile it in my macOS Catalina v10.15.2. I am using the latest version of gcc. The message I am receiving when trying to compile is :
Undefined symbols for architecture x86_64: "_main", referenced from:
implicit entry/start for main executable ld: symbol(s) not found for architecture x86_64 collect2: error: ld returned 1 exit status
So far I have tried to change _start to start but still getting the same result. As I understand the compilation process is different depending on the OS.
Note: There is no problem I am trying to solve here , just curiosity.
Thank you in advance
On macOS 10.14.6 with Xcode 11.3, the code in the question compiles and links with the command:
clang -Wl,-e, -Wl,__start <Name of Your Source File>
The resulting executable appears to work. However, since it bypasses the startup code for the C environment, you should not expect that using routines from the C library or other C features will work properly.
Note that two underscores are needed before start in the above command because the source code contains one and another is added by the C compiler. If the code is changed to use start instead of _start, then the command would use one underscore:
clang -Wl,-e, -Wl,_start <Name of Your Source File>
The switches -Wl,-e, -Wl,_start pass -e _start to the linker, which tells it to use _start as the address of the initial code to execute. It is not clear to me why this bypasses the default loading of the C-run-time-startup object module, which also defines _start. I would have preferred to use a linker switch that tells it not to load that module, but I did not find one in the man page for ld. Experimentation suggests that, by default, ld loads the default object module, and it refers to main, which results in a link error, but, when -e _start is used, the linker sets the program’s _start symbol as the startup address and does not load the default object module.
I'm pretty sure you can compile any C-source without main().
The problem will be with the linker trying to create an executable, which won't work without main().
I have a header file included in the main but when I compile the main, I have an error saying that the linker failed.
I tried to find the object files but I cannot find them.
I think the problem may come from my machine. I am kind of a beginner so I don't know how to solve this
When I try compiling my code I get this error:
Undefined symbols for architecture x86_64:
"_intClassic", referenced from:
_main in main-53b7e4.o
"_intQuadrature", referenced from:
_main in main-53b7e4.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
#zwol #JonathanLeffer I have 3 files in my project main.c, integral.h
and integral.c. integral.c contains the code of the functions
intClassic and intQuadrature that allow me to calculate different
types of integral. In integral.h I declared the functions and
structures I use. Finally in the main I included integral.h .
Also $ gcc -o output file1.o file2.o can this command help me ?
In the same directory as your files, try running the command
gcc main.c integral.c -o integral
This should take the 2 files and compile them into a program called ./integral
I have a MATLAB function that has signal processing and machine learning and I wanted to test it on another OS like linux. So I use codegen to generate C code for that function. When I come to run it (predictActivityFromSignalBuffer) on the command line, this is what I get:
MacBook-Pro-2:predictActivityFromSignalBuffer kareem$ gcc predictActivityFromSignalBuffer.c
Undefined symbols for architecture x86_64:
"_featuresFromBuffer", referenced from:
_predictActivityFromSignalBuffer in predictActivityFromSignalBuffer-1a1886.o
"_main", referenced from:
implicit entry/start for main executable
"_mynn", referenced from:
_predictActivityFromSignalBuffer in predictActivityFromSignalBuffer-1a1886.o
"_rtIsNaN", referenced from:
_predictActivityFromSignalBuffer in predictActivityFromSignalBuffer-1a1886.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
What is this error telling me exactly? I have no idea how to debug this or where to start/look.
Did you really just call
$ gcc predictActivityFromSignalBuffer.c
without any other dependencies? Usually there come a lot of other files with a code generation that have to be linked.
I do not know what you have done to produce your .c file. I recommend to use the coder wizard by typing
coder
in the Matlab command window. This will guide you through the whole process of code generation and also offers a lot of support and testing possibilities. You can also choose to compile your functions to ready-to-use DLL libraries or executatables. Just have a look at it.
I'm having some trouble somewhere with the linker while trying to compile a test written using the Unity testing framework by Throw The Switch. I have other tests that compile and run perfectly fine so I'm definitely just missing something in enabling the assertion helper for double floating point comparisons.
There is documentation in the header file telling us how to enable double floating point comparisons.
* - define UNITY_INCLUDE_DOUBLE to allow double floating point comparisons
However, I end up with this error:
Undefined symbols for architecture x86_64:
"_UnityAssertDoublesWithin", referenced from:
_test_example in main-6fae82.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
I wrote up the simplest example possible to duplicate this:
#define UNITY_INCLUDE_DOUBLE
#include "unity.h"
void test_example(void)
{
TEST_ASSERT_EQUAL_DOUBLE(1.234, 1.234);
}
int main(void) {
UNITY_BEGIN();
RUN_TEST(test_example);
return UNITY_END();
}
The contents of the CWD of the example and the exact command used to call clang (showing the same error again):
$ ls
main.c unity.c unity.h unity_internals.h
$ clang unity.c main.c
Undefined symbols for architecture x86_64:
"_UnityAssertDoublesWithin", referenced from:
_test_example in main-ee77c2.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
Same exact thing happens with gcc (but it's actually just calling clang under the hood).
I'm pretty sure I'm just missing one tiny step but for the life of me I can't see what it is right now. Thanks in advance for your help.
I have this working on my minimal tests by using the same define in the unity_config.h file and adding UNITY_INCLUDE_CONFIG_H as a compiler -D flag (gcc). But running with the #define in the source does not do the same trick
You can find a full copy of a unity_config.h file on the ThrowTheSwitch GitHub repo. I usually just throw it in the same folder Unity is in.
It also works if you add the define directly into the unity.h file as specified in the comments in that file (that you quote in your question) which says
All options described below should be passed as a compiler flag to all files using Unity. If you must add #defines, place them BEFORE the #include above.
i.e. in unity.h
#define UNITY_INCLUDE_DOUBLE
#include "unity_internals.h"
...
Why your initial tactic, which should essentially be the same thing, does not work, I do not know.
Looks like this works when defining UNITY_INCLUDE_DOUBLE with the -D flag to clang/gcc. For example:
$ clang -DUNITY_INCLUDE_DOUBLE -DUNITY_DOUBLE_PRECISION=1e-12f unity.c main.c
$ ./a.out
main.c:10:test_example:PASS
-----------------------
1 Tests 0 Failures 0 Ignored
OK
I am trying to compile a very simple C/C++ program to call Julia functions. Following the instructions that you find on the Julia documentation page, I set up my link path to /Users/william.calhoun/Desktop/romeo/lib/julia looking for libjulia.so and I set up my include path to /Users/william.calhoun/Desktop/romeo/include/julia looking for julia.h
I have a C file called test.c which runs the following code:
#include <stdio.h>
#include "skeleton.h"
#include <julia.h>
int main(int argc, const char * argv[]) {
jl_init(NULL);
/* run julia commands */
jl_eval_string("print(sqrt(2.0))");
/* strongly recommended: notify julia that the
program is about to terminate. this allows
julia time to cleanup pending write requests
and run all finalizers
*/
jl_atexit_hook();
return 0;
}
However this yields the following error:
Undefined symbols for architecture x86_64:
"_jl_atexit_hook", referenced from:
_main in test.o
"_jl_eval_string", referenced from:
_main in test.o
"_jl_init", referenced from:
_main in test.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
I am not doing anything other than calling functions defined properly (hopefully) within the Julia source code. What am I doing wrong? This seems like the simplest example and I can't figure it out.
Any help would be much appreciated!
Linking to libjulia (libjulia.dynlib on OS/X)
This error is a result of not linking to libjulia, as all of the symbols (_jl_atexit_hook, _jl_eval_string, _jl_init) are located in that library. Broadly, for all 3 of the following platforms (Windows, OS/X, Linux), the approach is similar, and though the location of the libjulia library is different on Windows than the other 2 this stackoverflow question is applicable. Also to be completely accurate, on OS/X, dynamic libraries have the extension .dynlib not .so as they do on Linux.
The link step
For simplicity, assuming you've compiled to object code (there is a file called embed.o), here's the link step.
cc -o embed embed.o -L/Users/william.calhoun/Desktop/romeo/lib/julia -Wl,-rpath,/Users/william.calhoun/Desktop/romeo/lib/julia -ljulia
There are 2 important things to note here.
Linking using -ljulia will allow the linker to resolve all of the above symbols.
Since this is a dynamic library and that dynamic library is located in a non standard location (e.g. not in /usr/lib), the dynamic linker will not be able to find it at run time unless you give it special instructions on how to find it. The -rpath directive causes the linker to insert the path /Users/william.calhoun/Desktop/romeo/lib/juliainto the list of paths to search.