DDMathParser in Objective-C++ produces error

Question

everybody, I am new to Stack Overflow (and DDMathParser), but came here because of a weird problem that occurred when I was trying to use DDMathParser in an objective-c++ file (main.mm). No matter how simple the code was, it would give a thread error. Here's my code:

#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <ctype.h>
#include <math.h>
#include <iostream>
#import "DDMathParser.h"
#import "NSString+DDMathParsing.h"
#import <Cocoa/Cocoa.h>
#import <Foundation/Foundation.h>

int main(int argc, char * argv[])
{
    NSLog(@"%@", [@"5 + 5" numberByEvaluatingString]);
}

And here's the console after running:

2015-08-29 09:23:09.788 calculator[6212:101522] -[__NSCFConstantString            numberByEvaluatingString]: unrecognized selector sent to instance 0x100001060
2015-08-29 09:23:09.792 calculator[6212:101522] *** Terminating app due to     uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFConstantString    numberByEvaluatingString]: unrecognized selector sent to instance 0x100001060'
*** First throw call stack:
(
    0   CoreFoundation                      0x00007fff9365d03c   __exceptionPreprocess + 172
    1   libobjc.A.dylib                     0x00007fff8fddd76e   objc_exception_throw + 43
    2   CoreFoundation                      0x00007fff936600ad -  [NSObject(NSObject) doesNotRecognizeSelector:] + 205
    3   CoreFoundation                      0x00007fff935a5e24   ___forwarding___ + 1028
    4   CoreFoundation                      0x00007fff935a5998   _CF_forwarding_prep_0 + 120
    5   calculator                          0x0000000100000e86 main + 38
    6   libdyld.dylib                       0x00007fff864595c9 start + 1
)
libc++abi.dylib: terminating with uncaught exception of type NSException
(lldb) 

Any suggestions?

Answer 1

You are not getting a "thread error." The ObjC runtime is throwing an exception because you are sending a message to an object, and that object does not implement the message.

Specifically, you are trying to invoke the selector numberByEvaluatingString on an instance of __NSCFConstantString, which can be thought of for this purpose as NSString.

Now, since you include the header files that define the method as a category on NSString, you don't get a compile error. However, at runtime, when the ObjC runtime environment sends the selector to the object, it can't find the implementation so it throws an exception.

This most likely means that you did not build and link the DDMathParser library with the little sample program. Thus, the implementation code is is unavailable at runtime.