This question already has answers here:
What is an undefined reference/unresolved external symbol error and how do I fix it?
(39 answers)
Closed 8 years ago.
the full message is:
error LNK2019 : unresolved external symbol "__declspec(dllimport)
public: virtual __cdecl FRenderResource::~FRenderResource(void)"
(__imp_ ? ? 1FRenderResource##UEAA#XZ) referenced in function "int
public: __cdecl FIndexBuffer::FIndexBuffer(class dtor$0 const
&)'::1'::dtor$0" (? dtor$0# ? 0 ? ? ?
0FIndexBuffer##QEAA#AEBV0##Z#4HA)
It appears when I write like this:
FRawStaticIndexBuffer indBuffer = obj->StaticMesh->RenderData->LODResources[0].IndexBuffer;
But if I change it to this:
FRawStaticIndexBuffer* indBuffer = &obj->StaticMesh->RenderData->LODResources[0].IndexBuffer;
everything fine. But what's the difference? Why pointer is safe and copy not?
"Why pointer is safe and copy not?"
Neither is safe.
With the copy, you have the error that a destructor has not been defined. (Missing symbol)
With the pointer, even though your program currently runs without a noticeable problem, you have the error that a destructor has not been called. (Memory/resource leak)
You need to find out why your linker isn't finding the definition to FRenderResource::~FRenderResource() anywhere, even though you declared it.
It's because a pointer is a memory address so if you take a memory address of some object (the part to the right of the equal sign) and store it in a pointer (which is a memory address object) then you're just saving a memory address to a memory address object so it'll always work.
It's like this: Bob lives at 123 Fake Street. 123 Fake Street is a pointer to Bob. Bob may or may not be home, but his house is always there. If Bob isn't home and you try to get Bob by going into his home then his security alarm will go off.
I agree that none of this is safe, but this explains what is happening.
Related
I'm migrating a XLL from 32-Bit to 64-Bit with VS2015 and C++.
I started changing the datatypes. So I switched 'int' to '_int64'.
CPP_XLOPER Create_XLOperHeader_form_Str(const wchar_t*aBegin,_int64 strlen,bool aTranspose){
static CPP_XLOPER xlDefault(L" ");
_int64 l = strlen;
and it throws me the error:
Error
LNK2001 unresolved external symbol
"class CPP_XLOPER __cdecl Create_XLOperTable_from_Str(wchar_t const *,__int64,bool,bool)"
(?Create_XLOperTable_from_Str##YA?AVCPP_XLOPER##PEB_W_J_N2#Z)
I guess I have to modify 'class CPP_XLOPER', isn't it?
Any hint much appreciated,
thx in advance;
surplus
The method linker is complaining about has last two parameters of type bool - ...,int64,bool,bool), while the one you have modified has only one last parameter of type bool. Either you have deleted another existing method, or you have also removed one bool from the implementation (and only you know if this was or was not intentional). But yeah, in general you should fix the function declaration to match the definition.
New to C++ programming I am trying to get some open source software running so I can build upon it.
I have 3 *cpp modules. One contains...
const double Qcf[6]= { 1.0, 448.831, 0.64632,0.02832, 28.317, 2.4466};
The other two modules make use of this constant and have a reference to it included in their body
extern double Qcf[];
Each of these modules then has a method/ function
i.e. something like
void routine1()
{
double i;
i = 2 * Qcf[1];
}
I have built the code and it appears that it has compiled (i.e. the *cpp goes to obj) but I get 2 error messages.
LNK2001 unresolved external symbol "double Qcf"
Each error pertains to each of the *obj files
(I also get another LNK1120 Two unresolved externals error, but I think if I solve the LNK2001 issue this will self correct).
Any advice on how to correct this is appreciated in advance.
Qcf is defined as a const double[] in one module, and declared as double[] in the other. You should declare it const too.
(or std::array<double, 6> instead of a C-style array, if your compiler supports C++11)
This question already has answers here:
What is an undefined reference/unresolved external symbol error and how do I fix it?
(39 answers)
Closed 7 years ago.
I am debugging some C++ software, and want to modify an existing function slightly, so that it changes the value of a particular variable used elsewhere in the program.
The function is currently defined as so:
void DataStore::setEraseSelected(){
...
// Function code here
...
}
As it stands, the function works correctly with no problems whatsoever. But, I now want to modify the function, so that it will change the value of a variable used elsewhere in the program. To do this, I have tried passing the variable into the function as a parameter (I have also updated the header file to reflect the changes to the function), and then assigning a value to the variable inside the function:
void DataStore::setEraseSelected(toAMS::DataMessage statusMsg){
...
// Function code here
...
statusMsg.CODE_ERASE = Types::Activated;
...
}
As mentioned, I have added the declaration to the header file, so that it now has the declaration for the function with the parameter, as well as the one for the function without the parameter:
void DataStore::setEraseSelected(toAMS::DataMessage statusMsg);
But when I try and build the code (using Visual Studio 2010), I get the following two compile errors:
error LNK2001: unresolved external symbol "public void_thiscall DataStore::setEraseSelected(void)" (? setEraseSelected#DataStore::QAEXXZ)
error LNK1120: 1 unresolved externals
The first error highlights the project .obj file, which I have tried deleting and building again, but get the same error, and second one highlights the project .exe file, which I have also tried deleting and building again, but get the same error.
Anyone have any ideas why? I've had a look on SO for questions regarding these errors, but none of them seem to clearly explain why I might be getting them. They all seem to suggest that the compiler is possibly looking in the wrong place, but if I undo my changes, then the code compiles with no problems, and I haven't told the compiler to look anywhere else when building the code with my changes...
void DataStore::setEraseSelected(int );
Pass that variable
I have try all solutions appeared on the web, but the error still exist.
Here are the error information:
error LNK2019: unresolved external symbol _gluOrtho2D#16 referenced in function "protected: virtual void __thiscall widget::initializeGL(void)" (?initializeGL#widget##MAEXXZ)
I am sure that I have included all the head files correctly, and link files are in their right position, and I also add #define GLUT_DISABLE_ATEXIT_HACK in my file. Besides, when I didn't use Qt, every thing is OK. While I put my code into QGLWidget, the error appeared!
Any more, I noticed that the error information after _gluOrtho2D# is 16, not 32 as other's on the web...
Why? How to correct them?
To answer your question regarding the 16 following the decorated _gluOrhto2D#, that is the size of the argument list you are passing (in bytes) when using the __stdcall calling convention.
Considering gluOrtho2D (...) is supposed to take 4 GLdouble arguments and GLdouble is supposed to be a 64-bit type something seems seriously wrong (the proper decorated name is _gluOrtho2D#32).
Did you by any chance confuse your compiler by attempting to pass gluOrtho2D (...) 4 GLfloat / float variables and/or re-define the prototype for gluOrtho2D (...) anywhere?
I think I have a problem with the getline function giving me an error to do with charcters.
The error I'm getting is:
Error 1 error LNK2019: unresolved external symbol "public: void __thiscall ArrayStorage::read(class std::basic_ifstream<char,struct std::char_traits<char> > &)" (?read#ArrayStorage##QAEXAAV?$basic_ifstream#DU?$char_traits#D#std###std###Z) referenced in function _main C:\Users\Lewis\SVN\project1\main.obj
Any ideas would be appreciated please. If anyone has a more effecient way of doing this task using this type of array I would take on any advice given.
blah blah blah unresolved external symbol "public: void __thiscall ArrayStorage::read (class std::basic_ifstream<char,struct std::char_traits<char> > &)" blah blah blah
This is a linker error. It means that a definition for the function ArrayStorage::read is missing. Why? Because the code has a definition of a function named read, not ArrayStorage::read. It should find it if you define ArrayStorage::read:
//Array cpp:
void ArrayStorage::read(ifstream& fin)
// ...
Once you get past that, the program will probably be able to run. And you'll probably find bugs because of the read loop. while (! fin.eof() ) doesn't "[run] while the file is NOT at the end". It runs while the previous read operation didn't try to read past the end. Consider what must have already happened by the time that check is made:
while (! fin.eof() ) // in the last iteration the read didn't go beyond the end of the file
{ // so one more iteration is ran
getline (fin,line); // tries to read past the end, fails
if (line == "") continue; // line is unchanged, so it could be a non-blank line from before
myArray[arrayIndex]=line; // Saves that line in the array:
// even though no line was read
arrayIndex++;
} // goes back to the start of the loop, and only now !fin.eof() fails
// but it's too late, the damage has been done
You probably don't want this to happen. You want to stop reading as soon as reading fails. That's simple: just put the reading as the condition:
while (getline (fin,line)) // if reading a line fails, the loop is not entered
{ // and so no extra line is added to the array
You're not providing a definition for the Array::read() function. You're declaring a new function that has the name read(), but is unrelated to the Array class. The compiler and linker don't care that it's in a file named Array.cpp.
Try this instead:
void Array::read(ifstream& fin)
{
//...
}
If I recall, this linker error can sometimes result from your class or one of its bases having other virtual functions that are undefined. The error occurs on the function named, rather than the virtual function that's actually missing a definition, because the MSVC compiler waits until it finds the first CPP file with a defined virtual function for the class to stick definitions of class-header-defined functions in, and when it doesn't find such a CPP file, it never defines the class-header-defined function. GCC behaves differently than MSVC in this respect; I believe GCC sticks the definitions in every object file they're used, and discards extras at link time. MSVC defines it only once, hence is subject to accidently never defining it. The reason it can't "just know" that it "forgot" to insert the definition is because the compiler can be invoked incrementally at any time, on only some of the files at one time, so it doesn't have the big picture.