Runtime error when compiling Objective-C project using g++ - c++

Question

I've made a really small project using Objective-C, and If I run it with the Xcode, It works really well.
But, I need to compile it using below command lines:
g++ Main.mm -o Main `gnustep-config --objc-flags` `gnustep-config --base-libs` -O2 -DONLINE_JUDGE -DBOJ
This command line is what the site I'm trying to upload my code to compile uses to compile Objective-C projects.
But, whenever I compile whit that command line, I get runtime errors for using NSMutableArray, NSSet and NSString.
Errors:
zsh: command not found: gnustep-config
zsh: command not found: gnustep-config
Undefined symbols for architecture x86_64:
"_OBJC_CLASS_$_NSMutableArray", referenced from:
objc-class-ref in Main-49f6e3.o
"_OBJC_CLASS_$_NSSet", referenced from:
objc-class-ref in Main-49f6e3.o
"_OBJC_CLASS_$_NSString", referenced from:
objc-class-ref in Main-49f6e3.o
"___CFConstantStringClassReference", referenced from:
CFString in Main-49f6e3.o
"_objc_msgSend", referenced from:
_main in Main-49f6e3.o
"_objc_opt_new", referenced from:
_main in Main-49f6e3.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
And, here is my source code:
#import <Foundation/Foundation.h>
int main(void) {
int num = 0;
int answer = 0;
scanf("%i", &num);
NSMutableArray *cl = [NSMutableArray new];
for (int k = 0; k < num; k++) {
char str[4];
getchar();
scanf("%[^\n]s", str);
NSString *userInput = [NSString stringWithUTF8String:str];
if (userInput.length == 1) {
[cl removeObjectAtIndex:0];
} else {
[cl addObject:[userInput substringFromIndex:[userInput length] - 1]];
}
NSMutableArray *result = [NSMutableArray new];
for (int i = 1; i <= cl.count; i++) {
for (int j = 0; j <= cl.count-i; j++) {
[result addObject:[[cl subarrayWithRange:NSMakeRange(j, i)] componentsJoinedByString:#""]];
}
}
answer += [[NSSet setWithArray:result] allObjects].count;
}
printf("%d\n", answer%1000000007);
return 0;
}

Answer 1

Those are linker errors, not runtime errors.
You need to link against the objc library and Foundation framework. Try:
g++ Main.mm -lobjc -framework Foundation ...