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?
have you tried
int main() or even int main(int argc, char**argv) ?
The error message indicates that the symbol _main (which refers to the main() function) is defined twice, once in helloworld.o and once in main.o.
It's likely that you have two source files, helloworld.c and main.c, in the same project, and that both define a function named main.
You can only have one main function in a program. Removing one of those two source files (and the associated object file) from your Xcode project should fix the problem. (I haven't used Xcode myself; perhaps someone else can tell you how to do that, if it's not obvious.)
(And the correct definition is int main(void), not the old-style main(), but I don't think that's related to the symptom you're seeing.)
There are a couple of stackoverflow questions that could be closely related to yours:
Xcode duplicate symbol _main
Xcode, Duplicate symbol _main
Related
I'm super new to coding I have downloaded Visual Studio and as I'm writing my first program I get this error
symbols for architecture x86_64:
"_main", referenced from:
implicit entry/start for main executable
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
I don't understand what to do. I have read in come post to see if I have a compiler and I believe I do
Apple clang version 13.0.0 (clang-1300.0.27.3)
Target: x86_64-apple-darwin21.4.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin
this was my code
#include <stdio.h>`int main() {printf("helloh world");return 0; }
You have a
`
in your code that's not needed and you lack white spaces between your include directive and your function declaration. Try it this way:
#include <stdio.h>
int main() {
printf("helloh world");
return 0;
}
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().
Sorry if this is a repeat question, but I couldn't find an answer that worked.
I'm writing a Hello World C program for the first time in a long time. I'm fairly certain the code is right, but it won't compile.
Running MAC OS 10.13.6 and I just downloaded XCode last week. The program compiles into an object file using
cc -c test.c -o test.o
without a problem. However, I can't create an executable using
cc test.o -o test
Here's the code:
#include <stdio.h>
int Main()
{
printf("Hello World");
return 0;
}
When I go to create the executable, I get
Undefined symbols for architecture x86_64:
"_main", referenced from:
implicit entry/start for main executable
ld: symbol(s) not found for architecture x86_64
I'm guessing I need to add some compiler flags but can't figure out which ones.
It sounds like you are just starting out in your journey into c code. This is a great opportunity to learn about c, compiling, and linking.
What you have written can compile just fine into an object file (containing a function called Main()). However, to link into an executable that can run from your OS, you need to define an entry point which is assumed to be a function called main (case sensitive as John mentioned above).
Check out this resource: http://www.ntu.edu.sg/home/ehchua/programming/cpp/gcc_make.html for an explanation of what the gcc compiler gets up to behind the scenes.
You just need to make a couple of small changes to get your code to work as expected:
#include <stdio.h>
int main(void) {
printf("Hello, world!\n");
return 0;
}
Main needs to be lowercase main.
While int main() will work, int main(void) is technically more accurate (see
void main(void) vs main())
You probably want a line new line after Hello, world!, so add the \n. (https://www.tutorialspoint.com/c_standard_library/c_function_printf.htm)
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.
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.