compiler-errors interview questions
Top compiler-errors frequently asked interview questions
I'm getting an error
Variable is not assignable (missing __block type specifier)
on the line aPerson = participant;. How can I make sure the block can access the aPerson variable and the aPerson variable can be returned?
Person *aPerson = nil;
[participants enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {
Person *participant = (Person*)obj;
if ([participant.gender isEqualToString:@"M"]) {
aPerson = participant;
*stop = YES;
}
}];
return aPerson;
Source: (StackOverflow)
I am trying to run some unit tests in a C# Windows Forms application (Visual Studio 2005) and I get the following error:
System.IO.FileLoadException: Could not load file or assembly 'Utility, Version=1.2.0.200, Culture=neutral, PublicKeyToken=764d581291d764f7' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)**
at x.Foo.FooGO()
at x.Foo.Foo2(String groupName_) in Foo.cs:line 123
at x.Foo.UnitTests.FooTests.TestFoo() in FooTests.cs:line 98**
System.IO.FileLoadException: Could not load file or assembly 'Utility, Version=1.2.0.203, Culture=neutral, PublicKeyToken=764d581291d764f7' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
I look in my references and I only have a reference to Utility version 1.2.0.203 (the other one is old).
Any suggestions on how I figure out what is trying to reference this old version of this DLL?
Besides, I don't think I even have this old assembly on my hard drive.
Is there any tool to search for this old versioned assembly?
Source: (StackOverflow)
I have imported framework for sending email from application in background. i have imported framework i.e. SKPSMTPMessage. Can somebody suggest me why I am getting this error
Undefined symbols for architecture i386:
"_OBJC_CLASS_$_SKPSMTPMessage", referenced from:
objc-class-ref in ConfirmController.o
"_kSKPSMTPPartContentTransferEncodingKey", referenced from:
-[ConfirmController sendEmail] in ConfirmController.o
"_kSKPSMTPPartMessageKey", referenced from:
-[ConfirmController sendEmail] in ConfirmController.o
"_kSKPSMTPPartContentTypeKey", referenced from:
-[ConfirmController sendEmail] in ConfirmController.o
ld: symbol(s) not found for architecture i386
collect2: ld returned 1 exit status
I have imported framework correctly.
Sorce from which i have taken framework and followed is:
Locking the Fields in MFMailComposeViewController
Update:
Answer is you just drag and drop folder over the project and click copy.
Thats it select project check box and target check box as well.
Source: (StackOverflow)
Recently I met the following exception at C# solution:
Error 2 Could not load file or assembly 'Newtonsoft.Json,
Version=3.5.0.0, Culture=neutral, PublicKeyToken=b9a188c8922137c6' or
one of its dependencies. The parameter is incorrect. (Exception from
HRESULT: 0x80070057 (E_INVALIDARG))
This does not depend either on my code or on the name of assembly (like Newtonsoft.Json in this case).
When I delete this dll from the solution the compiler tells about another in the same exception. So I suppose something shoud be turned off/on at my PC :)
Source: (StackOverflow)
Why does the first and second Write work but not the last? Is there a way I can allow all 3 of them and detect if it was 1, (int)1 or i passed in? And really why is one allowed but the last? The second being allowed but not the last really blows my mind.
Demo to show compile error
using System;
class Program
{
public static void Write(short v) { }
static void Main(string[] args)
{
Write(1);//ok
Write((int)1);//ok
int i=1;
Write(i);//error!?
}
}
Source: (StackOverflow)
I have a huge number of functions totaling around 2.8 GB of object code (unfortunately there's no way around, scientific computing ...)
When I try to link them, I get (expected) relocation truncated to fit: R_X86_64_32S errors, that I hoped to circumvent by specifing the compiler flag -mcmodel=medium. All libraries that are linked in addition that I have control of are compiled with the -fpic flag.
Still, the error persists, and I assume that some libraries I link to are not compiled with PIC.
Here's the error:
/usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../lib64/crt1.o: In function `_start':
(.text+0x12): relocation truncated to fit: R_X86_64_32S against symbol `__libc_csu_fini' defined in .text section in /usr/lib64/libc_nonshared.a(elf-init.oS)
/usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../lib64/crt1.o: In function `_start':
(.text+0x19): relocation truncated to fit: R_X86_64_32S against symbol `__libc_csu_init' defined in .text section in /usr/lib64/libc_nonshared.a(elf-init.oS)
/usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../lib64/crt1.o: In function `_start':
(.text+0x20): undefined reference to `main'
/usr/lib/gcc/x86_64-redhat-linux/4.1.2/../../../../lib64/crti.o: In function `call_gmon_start':
(.text+0x7): relocation truncated to fit: R_X86_64_GOTPCREL against undefined symbol `__gmon_start__'
/usr/lib/gcc/x86_64-redhat-linux/4.1.2/crtbegin.o: In function `__do_global_dtors_aux':
crtstuff.c:(.text+0xb): relocation truncated to fit: R_X86_64_PC32 against `.bss'
crtstuff.c:(.text+0x13): relocation truncated to fit: R_X86_64_32 against symbol `__DTOR_END__' defined in .dtors section in /usr/lib/gcc/x86_64-redhat-linux/4.1.2/crtend.o
crtstuff.c:(.text+0x19): relocation truncated to fit: R_X86_64_32S against `.dtors'
crtstuff.c:(.text+0x28): relocation truncated to fit: R_X86_64_PC32 against `.bss'
crtstuff.c:(.text+0x38): relocation truncated to fit: R_X86_64_PC32 against `.bss'
crtstuff.c:(.text+0x3f): relocation truncated to fit: R_X86_64_32S against `.dtors'
crtstuff.c:(.text+0x46): relocation truncated to fit: R_X86_64_PC32 against `.bss'
crtstuff.c:(.text+0x51): additional relocation overflows omitted from the output
collect2: ld returned 1 exit status
make: *** [testsme] Error 1
And system libraries I link against:
-lgfortran -lm -lrt -lpthread
Any clues where to look for the problem?
EDIT:
First of all, thank you for the discussion ...
To clarify a bit, I have hundreds of functions (each approx 1 MB in size in separate object files) like this:
double func1(std::tr1::unordered_map<int, double> & csc,
std::vector<EvaluationNode::Ptr> & ti,
ProcessVars & s)
{
double sum, prefactor, expr;
prefactor = +s.ds8*s.ds10*ti[0]->value();
expr = ( - 5/243.*(s.x14*s.x15*csc[49300] + 9/10.*s.x14*s.x15*csc[49301] +
1/10.*s.x14*s.x15*csc[49302] - 3/5.*s.x14*s.x15*csc[49303] -
27/10.*s.x14*s.x15*csc[49304] + 12/5.*s.x14*s.x15*csc[49305] -
3/10.*s.x14*s.x15*csc[49306] - 4/5.*s.x14*s.x15*csc[49307] +
21/10.*s.x14*s.x15*csc[49308] + 1/10.*s.x14*s.x15*csc[49309] -
s.x14*s.x15*csc[51370] - 9/10.*s.x14*s.x15*csc[51371] -
1/10.*s.x14*s.x15*csc[51372] + 3/5.*s.x14*s.x15*csc[51373] +
27/10.*s.x14*s.x15*csc[51374] - 12/5.*s.x14*s.x15*csc[51375] +
3/10.*s.x14*s.x15*csc[51376] + 4/5.*s.x14*s.x15*csc[51377] -
21/10.*s.x14*s.x15*csc[51378] - 1/10.*s.x14*s.x15*csc[51379] -
2*s.x14*s.x15*csc[55100] - 9/5.*s.x14*s.x15*csc[55101] -
1/5.*s.x14*s.x15*csc[55102] + 6/5.*s.x14*s.x15*csc[55103] +
27/5.*s.x14*s.x15*csc[55104] - 24/5.*s.x14*s.x15*csc[55105] +
3/5.*s.x14*s.x15*csc[55106] + 8/5.*s.x14*s.x15*csc[55107] -
21/5.*s.x14*s.x15*csc[55108] - 1/5.*s.x14*s.x15*csc[55109] -
2*s.x14*s.x15*csc[55170] - 9/5.*s.x14*s.x15*csc[55171] -
1/5.*s.x14*s.x15*csc[55172] + 6/5.*s.x14*s.x15*csc[55173] +
27/5.*s.x14*s.x15*csc[55174] - 24/5.*s.x14*s.x15*csc[55175] +
// ...
;
sum += prefactor*expr;
// ...
return sum;
}
The object s is relatively small and keeps the needed constants x14, x15, ..., ds0, ..., etc. while ti just returns a double from an external library. As you can see, csc[] is a precomputed map of values which is also evaluated in separate object files (again hundreds with about ~1 MB of size each) of the following form:
void cscs132(std::tr1::unordered_map<int,double> & csc, ProcessVars & s)
{
{
double csc19295 = + s.ds0*s.ds1*s.ds2 * ( -
32*s.x12pow2*s.x15*s.x34*s.mbpow2*s.mWpowinv2 -
32*s.x12pow2*s.x15*s.x35*s.mbpow2*s.mWpowinv2 -
32*s.x12pow2*s.x15*s.x35*s.x45*s.mWpowinv2 -
32*s.x12pow2*s.x25*s.x34*s.mbpow2*s.mWpowinv2 -
32*s.x12pow2*s.x25*s.x35*s.mbpow2*s.mWpowinv2 -
32*s.x12pow2*s.x25*s.x35*s.x45*s.mWpowinv2 +
32*s.x12pow2*s.x34*s.mbpow4*s.mWpowinv2 +
32*s.x12pow2*s.x34*s.x35*s.mbpow2*s.mWpowinv2 +
32*s.x12pow2*s.x34*s.x45*s.mbpow2*s.mWpowinv2 +
32*s.x12pow2*s.x35*s.mbpow4*s.mWpowinv2 +
32*s.x12pow2*s.x35pow2*s.mbpow2*s.mWpowinv2 +
32*s.x12pow2*s.x35pow2*s.x45*s.mWpowinv2 +
64*s.x12pow2*s.x35*s.x45*s.mbpow2*s.mWpowinv2 +
32*s.x12pow2*s.x35*s.x45pow2*s.mWpowinv2 -
64*s.x12*s.p1p3*s.x15*s.mbpow4*s.mWpowinv2 +
64*s.x12*s.p1p3*s.x15pow2*s.mbpow2*s.mWpowinv2 +
96*s.x12*s.p1p3*s.x15*s.x25*s.mbpow2*s.mWpowinv2 -
64*s.x12*s.p1p3*s.x15*s.x35*s.mbpow2*s.mWpowinv2 -
64*s.x12*s.p1p3*s.x15*s.x45*s.mbpow2*s.mWpowinv2 -
32*s.x12*s.p1p3*s.x25*s.mbpow4*s.mWpowinv2 +
32*s.x12*s.p1p3*s.x25pow2*s.mbpow2*s.mWpowinv2 -
32*s.x12*s.p1p3*s.x25*s.x35*s.mbpow2*s.mWpowinv2 -
32*s.x12*s.p1p3*s.x25*s.x45*s.mbpow2*s.mWpowinv2 -
32*s.x12*s.p1p3*s.x45*s.mbpow2 +
64*s.x12*s.x14*s.x15pow2*s.x35*s.mWpowinv2 +
96*s.x12*s.x14*s.x15*s.x25*s.x35*s.mWpowinv2 +
32*s.x12*s.x14*s.x15*s.x34*s.mbpow2*s.mWpowinv2 -
32*s.x12*s.x14*s.x15*s.x35*s.mbpow2*s.mWpowinv2 -
64*s.x12*s.x14*s.x15*s.x35pow2*s.mWpowinv2 -
32*s.x12*s.x14*s.x15*s.x35*s.x45*s.mWpowinv2 +
32*s.x12*s.x14*s.x25pow2*s.x35*s.mWpowinv2 +
32*s.x12*s.x14*s.x25*s.x34*s.mbpow2*s.mWpowinv2 -
32*s.x12*s.x14*s.x25*s.x35pow2*s.mWpowinv2 -
// ...
csc.insert(cscMap::value_type(192953, csc19295));
}
{
double csc19296 = // ... ;
csc.insert(cscMap::value_type(192956, csc19296));
}
// ...
}
That's about it. The final step then just consists in calling all those func[i] and summing the result up.
Concerning the fact that this is a rather special and unusual case: Yes, it is. This is what people have to cope with when trying to do high precision computations for particle physics.
EDIT2:
I should also add that x12, x13, etc. are not really constants. They are set to specific values, all those functions are run and the result returned, and then a new set of x12, x13, etc. is chosen to produce the next value. And this has to be done 10^5 to 10^6 times...
EDIT3:
Thank you for the suggestions and the discussion so far... I'll try to roll the loops up upon code generation somehow, not sure how to this exactly, to be honest, but this is the best bet.
BTW, I didn't try to hide behind "this is scientific computing -- no way to optimize".
It's just that the basis for this code is something that comes out of a "black box" where I have no real access to and, moreover, the whole thing worked great with simple examples, and I mainly feel overwhelmed with what happens in a real world application ...
EDIT4:
So, I have managed to reduce the code size of the csc definitions by about one forth by simplifying expressions in a computer algebra system (Mathematica). I see now also some way to reduce it by another order of magnitude or so by applying some other tricks before generating the code (which would bring this part down to about 100 MB) and I hope this idea works.
Now related to your answers:
I'm trying to roll the loops back up again in the funcs, where a CAS won't help much, but I have already some ideas. For instance, sorting the expressions by the variables like x12, x13,..., parse the cscs with Python and generate tables that relate them to each other. Then I can at least generate these parts as loops. As this seems to be the best solution so far, I mark this as the best answer.
However, I'd like to also give credit to VJo. GCC 4.6 indeed works much better, produces smaller code and is faster. Using the large model works at the code as-is. So technically this is the correct answer, but changing the whole concept is a much better approach.
Thank you all for your suggestions and help. If anyone is interested, I'm going to post the final outcome as soon as I am ready.
REMARKS:
Just some remarks to some other answers: The code I'm trying to run does not originate in an expansion of simple functions/algorithms and stupid unnecessary unrolling. What actually happens is that the stuff we start with is pretty complicated mathematical objects and bringing them to a numerically computable form generates these expressions. The problem lies actually in the underlying physical theory. Complexity of intermediate expressions scales factorially, which is well known, but when combining all of this stuff to something physically measureable -- an observable -- it just boils down to only a handful of very small functions that form the basis of the expressions. (There is definitely something "wrong" in this respect with the general and only available ansatz which is called "perturbation theory") We try to bring this ansatz to another level, which is not feasible analytically anymore and where the basis of needed functions is not known. So we try to brute-force it like this. Not the best way, but hopefully one that helps with our understanding of the physics at hand in the end...
LAST EDIT:
Thanks to all your suggestions, I've managed to reduce the code size considerably, using Mathematica and a modification of the code generator for the funcs somewhat along the lines of the top answer :)
I have simplified the csc functions with Mathematica, bringing it down to 92 MB. This is the irreducible part. The first attempts took forever, but after some optimizations this now runs through in about 10 minutes on a single CPU.
The effect on the funcs was dramatic: The whole code size for them is down to approximately 9 MB, so the code now totals in the 100 MB range. Now it makes sense to turn optimizations on and the execution is quite fast.
Again, thank you all for your suggestions, I've learned a lot.
Source: (StackOverflow)
Having a bit of trouble with the syntax where we want to call a delegate anonymously within a Control.Invoke.
We have tried a number of different approaches, all to no avail.
For example:
myControl.Invoke(delegate() { MyMethod(this, new MyEventArgs(someParameter)); });
where someParameter is local to this method
The above will result in a compiler error:
Cannot convert anonymous method to type 'System.Delegate' because it is not a delegate type
Source: (StackOverflow)
I often find myself in a situation where I am facing multiple compilation/linker errors in a C++ project due to some bad design decisions (made by someone else :) ) which lead to circular dependencies between C++ classes in different header files (can happen also in the same file). But fortunately(?) this doesn't happen often enough for me to remember the solution to this problem for the next time it happens again. So for the purposes of easy recall in the future I am going to post a representative problem and a solution along with it (I hope this is not against the rules of stackoverflow). Better solutions are of-course welcome.
Source: (StackOverflow)
Compiled with VS 2012, with project type WP 8.0 the following code will fail if debugger is not attached.
Somehow, if debugger not attached, compiler optimizations ruins the code inside Crash() - see comments in code.
Tested on Lumia 1520 (8.1) and Lumia 630 (8.0).
Any ideas why this is occurring?
public partial class MainPage : PhoneApplicationPage
{
public MainPage()
{
InitializeComponent();
Button.Tap += (sender, args) => new A<B, string>(new B(), "string").Crash();
}
}
public class B
{
public void Foo<T>(T val) { }
}
public class A<T1, T2> where T1 : B
{
private T1 _t1;
private T2 _t2;
public A(T1 t1, T2 t2)
{
_t2 = t2;
_t1 = t1;
}
public void Crash()
{
var obs = Observable.Return(_t2);
obs.Subscribe(result =>
{
//CLR is expecting T2 to be System.String here,
//but somehow, after passing through Observable
//T2 here is not a string, it's A<T1, T2>
new List<T2>().Add(result);
});
//Will run normally if commented
_t1.Foo(new object());
}
}
Source: (StackOverflow)
The following code has a static method, Foo(), calling an instance method, Bar():
public sealed class Example
{
int count;
public static void Foo( dynamic x )
{
Bar(x);
}
void Bar( dynamic x )
{
count++;
}
}
It compiles without error* but generates a runtime binder exception at runtime. Removing the dynamic parameter to these methods causes a compiler error, as expected.
So why does having a dynamic parameter allow the code to be compiled? ReSharper doesn't show it as an error either.
Edit 1: *in Visual Studio 2008
Edit 2: added sealed since it's possible that a subclass could contain a static Bar(...) method. Even the sealed version compiles when it's not possible that any method other than the instance method could be called at runtime.
Source: (StackOverflow)
I'm having another of these "Could not load file or assembly or one of its dependencies" problems.
Additional information: Could not load
file or assembly
'Microsoft.Practices.Unity,
Version=1.2.0.0, Culture=neutral,
PublicKeyToken=31bf3856ad364e35' or
one of its dependencies. The located
assembly's manifest definition does
not match the assembly reference.
(Exception from HRESULT: 0x80131040)
I have no idea what is causing this or how I could debug it to find the cause.
I've done a search in my solution catalogs .csproj files, and every where I have Unity I have:
Reference
Include="Microsoft.Practices.Unity,
Version=2.0.414.0, Culture=neutral,
PublicKeyToken=31bf3856ad364e35,
processorArchitecture=MSIL"
Can't find any reference anywhere which goes against 1.2.0.0 in any of my projects.
Any ideas how I should go about solving this?
I would also appreciate tips on how to debug problems like this in general.
Source: (StackOverflow)
This question already has an answer here:
I have no idea why this is happenning, since I think I have everything properly declared and defined.
I have the following program, designed with templates. It's a simple implementation of a queue, with the member functions "add", "substract" and "print".
I have defined the node for the queue in the fine "nodo_colaypila.h":
#ifndef NODO_COLAYPILA_H
#define NODO_COLAYPILA_H
#include <iostream>
template <class T> class cola;
template <class T> class nodo_colaypila
{
T elem;
nodo_colaypila<T>* sig;
friend class cola<T>;
public:
nodo_colaypila(T, nodo_colaypila<T>*);
};
Then the implementation in "nodo_colaypila.cpp"
#include "nodo_colaypila.h"
#include <iostream>
template <class T> nodo_colaypila<T>::nodo_colaypila(T a, nodo_colaypila<T>* siguiente = NULL)
{
elem = a;
sig = siguiente;//ctor
}
Afterwards, the definition and declaration of the queue template class and its functions:
"cola.h":
#ifndef COLA_H
#define COLA_H
#include "nodo_colaypila.h"
template <class T> class cola
{
nodo_colaypila<T>* ult, pri;
public:
cola<T>();
void anade(T&);
T saca();
void print() const;
virtual ~cola();
};
#endif // COLA_H
"cola.cpp":
#include "cola.h"
#include "nodo_colaypila.h"
#include <iostream>
using namespace std;
template <class T> cola<T>::cola()
{
pri = NULL;
ult = NULL;//ctor
}
template <class T> void cola<T>::anade(T& valor)
{
nodo_colaypila <T> * nuevo;
if (ult)
{
nuevo = new nodo_colaypila<T> (valor);
ult->sig = nuevo;
ult = nuevo;
}
if (!pri)
{
pri = nuevo;
}
}
template <class T> T cola<T>::saca()
{
nodo_colaypila <T> * aux;
T valor;
aux = pri;
if (!aux)
{
return 0;
}
pri = aux->sig;
valor = aux->elem;
delete aux;
if(!pri)
{
ult = NULL;
}
return valor;
}
template <class T> cola<T>::~cola()
{
while(pri)
{
saca();
}//dtor
}
template <class T> void cola<T>::print() const
{
nodo_colaypila <T> * aux;
aux = pri;
while(aux)
{
cout << aux->elem << endl;
aux = aux->sig;
}
}
Then, I have a program to test these functions as follows:
"main.cpp"
#include <iostream>
#include "cola.h"
#include "nodo_colaypila.h"
using namespace std;
int main()
{
float a, b, c;
string d, e, f;
cola<float> flo;
cola<string> str;
a = 3.14;
b = 2.71;
c = 6.02;
flo.anade(a);
flo.anade(b);
flo.anade(c);
flo.print();
cout << endl;
d = "John";
e = "Mark";
f = "Matthew";
str.anade(d);
str.anade(e);
str.anade(f);
cout << endl;
c = flo.saca();
cout << "First In First Out Float: " << c << endl;
cout << endl;
f = str.saca();
cout << "First In First Out String: " << f << endl;
cout << endl;
flo.print();
cout << endl;
str.print();
cout << "Hello world!" << endl;
return 0;
}
But when I build, the compiler throws errors in every instance of the template class:
undefined reference to `cola(float)::cola()'... (it's actually cola'<'float'>'::cola(), but this doesn't let me use it like that.)
And so on. Altogether, 17 warnings, counting the ones for the member functions being called in the program.
Why is this? Those functions and constructors WERE defined. I thought that the compiler could replace the "T" in the template with "float", "string" or whatever; that was the advantage of using templates.
I read somewhere here that I should put the declaration of each function in the header file for some reason. Is that right? And if so, why?
Thanks in advance.
Source: (StackOverflow)
The following code gives you a compiler error, as you'd expect:
List<Banana> aBunchOfBananas = new List<Banana>();
Banana justOneBanana = (Banana)aBunchOfBananas;
However, when using IEnumerable<Banana>, you merely get a runtime error.
IEnumerable<Banana> aBunchOfBananas = new List<Banana>();
Banana justOneBanana = (Banana)aBunchOfBananas;
Why does the C# compiler allow this?
Source: (StackOverflow)
I have the following generic method, but VS gives me a compile error on that. (Operator '??' cannot be applied to operands of type 'T' and 'T')
public static T Method<T>(T model) where T : new()
{
var m = model ?? new T();
}
Does some one have any idea why?
Edit: Is it possible the reason is that T can be a struct in my case, and a struct is an non-nullable type?
Source: (StackOverflow)