Programming Forums > Application Development > C++

uman · Feb 5th, 2005, 2:15 PM

OK, after hours of debugging my program, I have finally found out where the problem lies. So you don't have to read through my whole program I will offer a simplified case that produces the same error. Please tell me why this error occurs and what I can do to stop it.

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//main.cpp
#include "FooClass.h"
main()
{
	int i=30;
	FooClass* pFoo;

	pFoo=(FooClass*)malloc(sizeof(FooClass)*i);
	pFoo[0].fooString="Foobar Quux";
}

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//FooClass.h
#pragma once
#include <string>
using namespace std;
class FooClass
{
public:
	string fooString;
	

};

This compiles fine, however it spits out errors when I try to run it. What is the problem?

Monster · Feb 5th, 2005, 3:34 PM

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main()
{
   int i=30;
   FooClass* pFoo;

   pFoo = new FooClass [i];
   pFoo[0].fooString="Foobar Quux";
   delete[] pFoo;
   return 0;
}

uman · Feb 5th, 2005, 4:01 PM

Yes, I know about vectors and use them whenever I can, however for what I am doing in my larger program I need arrays.

Thanks anyway for the help though.

Monster · Feb 5th, 2005, 4:08 PM

You beat me... just changed it to an array.

uman · Feb 5th, 2005, 4:09 PM

Ah, ok I understand now. Thanks a million for the help.

Monster · Feb 5th, 2005, 4:16 PM

Another example. In the first example you create an array with 30 FooClass objects. In this example you create an array with 30 pointers to FooClass objects. To add a FooClass, you need to allocate space for the class first.

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main()
{
   int i=30;
   FooClass** pFoo;

   pFoo = new FooClass *[i]; // create array with 30 pointers
   pFoo[0] = new FooClass(); // create a new FooClass
   pFoo[0]->fooString="Foobar Quux";
   delete pFoo[0]; // delete the FooClass
   delete[] pFoo; // delete the array
   return 0;
}

Feb 5th, 2005, 2:15 PM	#1
uman Expert Programmer Join Date: Dec 2004 Posts: 794 Rep Power: 4	[solved]Simple problem with C++ dynamic memory allocation: please help. OK, after hours of debugging my program, I have finally found out where the problem lies. So you don't have to read through my whole program I will offer a simplified case that produces the same error. Please tell me why this error occurs and what I can do to stop it. (Toggle Plain Text) //main.cpp #include "FooClass.h" main() { int i=30; FooClass* pFoo; pFoo=(FooClass)malloc(sizeof(FooClass)i); pFoo[0].fooString="Foobar Quux"; } //main.cpp #include "FooClass.h" main() { int i=30; FooClass* pFoo; pFoo=(FooClass)malloc(sizeof(FooClass)i); pFoo[0].fooString="Foobar Quux"; } (Toggle Plain Text) //FooClass.h #pragma once #include <string> using namespace std; class FooClass { public: string fooString; }; //FooClass.h #pragma once #include <string> using namespace std; class FooClass { public: string fooString; }; This compiles fine, however it spits out errors when I try to run it. What is the problem? Last edited by uman; Feb 5th, 2005 at 4:10 PM. Reason: Added [solved] to title

Feb 5th, 2005, 3:34 PM	#2
Monster Newbie Join Date: Jan 2005 Posts: 20 Rep Power: 0	(Toggle Plain Text) main() { int i=30; FooClass* pFoo; pFoo = new FooClass [i]; pFoo[0].fooString="Foobar Quux"; delete[] pFoo; return 0; } main() { int i=30; FooClass* pFoo; pFoo = new FooClass [i]; pFoo[0].fooString="Foobar Quux"; delete[] pFoo; return 0; } Last edited by Monster; Feb 5th, 2005 at 4:05 PM.

Feb 5th, 2005, 4:16 PM	#6
Monster Newbie Join Date: Jan 2005 Posts: 20 Rep Power: 0	Another example. In the first example you create an array with 30 FooClass objects. In this example you create an array with 30 pointers to FooClass objects. To add a FooClass, you need to allocate space for the class first. (Toggle Plain Text) main() { int i=30; FooClass** pFoo; pFoo = new FooClass [i]; // create array with 30 pointers pFoo[0] = new FooClass(); // create a new FooClass pFoo[0]->fooString="Foobar Quux"; delete pFoo[0]; // delete the FooClass delete[] pFoo; // delete the array return 0; } main() { int i=30; FooClass* pFoo; pFoo = new FooClass *[i]; // create array with 30 pointers pFoo[0] = new FooClass(); // create a new FooClass pFoo[0]->fooString="Foobar Quux"; delete pFoo[0]; // delete the FooClass delete[] pFoo; // delete the array return 0; }

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Feb 5th, 2005, 4:01 PM	#3
uman Expert Programmer Join Date: Dec 2004 Posts: 794 Rep Power: 4	Yes, I know about vectors and use them whenever I can, however for what I am doing in my larger program I need arrays. Thanks anyway for the help though.

Feb 5th, 2005, 4:08 PM	#4
Monster Newbie Join Date: Jan 2005 Posts: 20 Rep Power: 0	You beat me... just changed it to an array.

Feb 5th, 2005, 4:09 PM	#5
uman Expert Programmer Join Date: Dec 2004 Posts: 794 Rep Power: 4	Ah, ok I understand now. Thanks a million for the help.

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Programming Forums > Application Development > C++

Simple problem with C++ dynamic memory allocation: please help.