Code that compiles for the iPhone Device but not for the Simulator

Question

I am using C++ to develop the algorithmic part of an iPhone application, and I am encountering a strange bug. The code that I have, compiles fine with gcc-4.2 both on Linux, on the Mac, and on the iPhone device, just not on the Simulator, which makes debugging and testing very difficult.

The error messages from the attempts to compile for the simulator resemble a known bug in 4.0.x, although that is not very clear why since I have explicitly set gcc-4.2 to be the default compiler.

To demonstrate the bug, I have prepared the following small code snippet:

bug.cpp

#include <tr1/unordered_map>
#include <iostream>

/* a hash key for the visitedTrip table */
struct X {
    int x;

    X() : x(0){};
    X(int x) : x(x){};
};


typedef std::tr1::unordered_map<int,X> dict;

int main() 
{ 
    dict c1; 

    X a(0);
    X b(1);
    X c(2);

    c1[0] = a;
    c1[1] = b;
    c1[2] = c;

    dict::const_iterator it;

    for(it = c1.begin(); it != c1.end(); it++)
     std::cout << it->first << std::endl;

    return (0); 
}

and then tried to compile it as follows:

compile.sh

#!/bin/bash

#
# Compiling for the simulator and compiling under gcc-4.0 return the same error message
#

#SUCCESS
c++-4.2 -arch i386 bug.cpp

#FAIL 
c++-4.0 -arch i386 bug.cpp

#SUCCESS
gcc-4.2 -arch i386 -c bug.cpp

#FAIL
gcc-4.0 -arch i386 -c bug.cpp

#FAIL
gcc-4.2 -arch i386 -c bug.cpp -isysroot /Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator3.1.sdk

Eventhough I am using gcc-4.2 to compile for the simulator, I am getting the same error message as if I were compiling under gcc-4.0, namely:

bug.cpp:27: error: no matching function for call to ‘Internal::hashtable_iterator<std::pair<const int, X>, false, false>::hashtable_iterator()’
/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator3.1.sdk/usr/include/c++/4.2.1/tr1/hashtable:236: note: candidates are: Internal::hashtable_iterator<Value, is_const, cache>::hashtable_iterator(const Internal::hashtable_iterator<Value, true, cache>&) [with Value = std::pair<const int, X>, bool is_const = false, bool cache = false]
/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator3.1.sdk/usr/include/c++/4.2.1/tr1/hashtable:234: note:                 Internal::hashtable_iterator<Value, is_const, cache>::hashtable_iterator(Internal::hash_node<Value, cache>**) [with Value = std::pair<const int, X>, bool is_const = false, bool cache = false]
/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator3.1.sdk/usr/include/c++/4.2.1/tr1/hashtable:232: note:                 Internal::hashtable_iterator<Value, is_const, cache>::hashtable_iterator(Internal::hash_node<Value, cache>*, Internal::hash_node<Value, cache>**) [with Value = std::pair<const int, X>, bool is_const = false, bool cache = false]
/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator3.1.sdk/usr/include/c++/4.2.1/tr1/hashtable:225: note:                 Internal::hashtable_iterator<std::pair<const int, X>, false, false>::hashtable_iterator(const Internal::hashtable_iterator<std::pair<const int, X>, false, false>&)

Any ideas as to why this gcc-4.0.x bug creeps into the simulator, when in fact the simulator is supposed to be using gcc-4.2.x where this bug has been fixed?

Answer 1

I would be checking carefully the library (STL) headers that the simulator is referencing.

Answer 2

Sometimes there are compiler issues in Xcode, maybe you have a problem analogous to the one described here.

UIKit SDK Error

In this case you have to specify the compiler specifically for device and simulator. I know that this doesn't make any sense but it fixed my problem.

Answer 3

Not sure if this is exactly the right answer, but this would probably explain why you're seeing the 4.0 behaviour while using 4.2:

> pwd
/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator3.1.sdk/usr/include/c++
> ls -l
total 4
drwxr-xr-x  10 root  wheel  2278 10 Sep 09:32 4.0.0/
lrwxr-xr-x   1 root  wheel     5 10 Sep 09:30 4.2.1@ -> 4.0.0

It looks like they're trying to use the 4.0 header set for both versions, at least on Snow Leopard with Xcode 3.2.

Answer 4

There's a problem with unordered_map's iterators not having default constructors in gcc-4.0.x

http://bytes.com/topic/c/answers/607427-error-tr1-unordered_map-iterator

Initialization upon declaration should fix it:

for(dict::const_iterator it = c1.begin(); it != c1.end(); it++)
    std::cout << it->first << std::endl;