Need help with Void*

[wd40bomber7]

The malfunctioning code snippet:

	ifstream uFile;
	struct stat results;
	char filePath[fileName.size()]; 
	chstr(fileName,*filePath);
	
	uFile.open(filePath, ios::in | ios::binary);
	
    if ( !uFile.is_open() )
    {
    	return false;
    }
    
    stat(filePath, &results);
    
    if (results.st_size <= 0)
    {
    	return false;
    }
    
    archFiles[fileAmt] = malloc(results.st_size+1);
    uFile.read(((char*)archFiles[fileAmt]),results.st_size);

I don't have a clue whats wrong with it!

Anyway, more in depth the last two lines are the problem.
Everytime it gets to uFile.read the program crashes.

A note:
archfiles is defined as such:

void * archFiles[];

I'm certain the problem lies in archFiles[fileAmt] but I haven't a clue whats wrong with it. Even an attempt to print out the value of the pointer (after the malloc ofc) results in a crash at the print statement!

Edit: More info, I'm using windows and my compiler is g++

[Paul McKenzie]

	ifstream uFile;
	struct stat results;
	char filePath[fileName.size()]; 
//...
void * archFiles[];

The code in red is illegal C++. You cannot define array sizes using variables, and you cannot define arrays as empty.

Use std::string to define string variables, and std::vector to define adjustable arrays.

my compiler is g++

That explains it. Turn off the extensions, and you will see that g++ will give you compiler errors (-Wall -pedantic). Otherwise, consult your g++ manual as to how to what those extensions do, as they are not legal C++.

Regards,

Paul McKenzie

[wd40bomber7]

Ok then, thanks for that. Do you have any suggestions on how to facilitate dynamic arrays?

I don't have a g++ manual. I acquired it through minGW. Also I'm using a programming environment called Wind River Work Bench. As far as I can tell there's no way to turn off any specific parameters from within the environment so I'll take your word for it.

Ok I changed

char filePath[fileName.size()];

to

char *filePath = (char*)malloc(fileName.size());
//...
free((void*)filePath);

Oh you said c++ doesn't allow for a variable to define an array size. What about in the following case?

int *a;
int n;
n = 25;
a = new int[n];

If that code works, my only problem would be expanding the array. The only solution to that, that I can think of is making a new array of the expanded size, copying all the data from the previous array to the new array then deleting the previous array.
Or perhaps I could make a linked list, though this is somewhat more difficult to deal with and has 4-8 bytes of necessary overhead per array entry.

Hmm after having thought about I'll probably go with a linked list of structs. The 8 bytes of overhead (per array element) is minor when being compared with the size of each array element.

[AlastrionaAdair]

Ok then, thanks for that. Do you have any suggestions on how to facilitate dynamic arrays?

use std::vector.

[Paul McKenzie]

To add, your code looks more like 'C' than C++. Usage of void* is not needed at all in the code you did show. Also, malloc() in a supposedly trivial C++ code is dubious, at best.

Another thing as that you never mentioned where "fileAmt" comes from. It just looks like you want to read something into a buffer, and the size of the buffer is determined by some runtime value.

#include <string>
#include <vector>
#include <fstream>
//... Other includes
typedef std::vector<std::vector<char> > ArrayofCharArray;

using namespace std;
ArrayofCharArray archFiles;

void someFunction()
{
   ifstream uFile;
   stat results;
   string filePath;
   //...
  uFile.open(filePath, ios::in | ios::binary);
	
   if ( !uFile.is_open() )
   {
    	return false;
    }
    
    stat(filePath.c_str(), &results);
    
    if (results.st_size <= 0)
    {
    	return false;
    }
    
    // Add an array of char to the vector
    archFiles.push_back(vector<char>());

    // Get the new array as a pointer for convenience
    std::vector<char>* buffer = &archFiles.back();

    // Resize it
    buffer->resize(results.st_size+1));

    // Use it in function
    uFile.read(&buffer->front(), results.st_size);
}

You now have an "array" of char arrays in archFiles. There is no call to malloc(), and the code is standard C++.

To get the data archFiles[0] is the buffer that contains the first line. archFiles[0].size() is the number of characters in the first line. archFiles[1] is the second line, etc.

Regards,

Paul McKenzie

[Paul McKenzie]

Ok then, thanks for that. Do you have any suggestions on how to facilitate dynamic arrays?

I stated to use std::vector. That is the dynamic array in C++ (see my example).

As far as I can tell there's no way to turn off any specific parameters from within the environment so I'll take your word for it.

You must be able to do that somehow. The g++ compiler relies on proper setting of command-line parameters, both by the IDE and by users. If not, then the IDE is worthless.

Ok I changed

char filePath[fileName.size()];

to

char *filePath = (char*)malloc(fileName.size());
//...
free((void*)filePath);

That is still 'C'. I stated to use std::string, which is the C++ way of defining strings.

Oh you said c++ doesn't allow for a variable to define an array size. What about in the following case?

int *a;
int n;
n = 25;
a = new int[n];

'a' is not an array. It is a pointer to an integer. Two different things altogether.

If that code works, my only problem would be expanding the array. The only solution to that, that I can think of is making a new array of the expanded size, copying all the data from the previous array to the new array then deleting the previous array.

Get a good C++ (not 'C') book. The std::vector class should (must) be explained there, as all of this is done automatically for you.

Regards,

Paul McKenzie

[Speedo]

Also I'm using a programming environment called Wind River Work Bench. As far as I can tell there's no way to turn off any specific parameters from within the environment so I'll take your word for it.

If it doesn't even allow you to change compiler settings you just need to trash it and go with something else (Code::Blocks and Visual Studio are the popular choices).

[wd40bomber7]

I find it very important to note
uFile.open(filePath, ios::in | ios::binary);
can not accept a string as its first parameter.

As for the rest of the code I am looking it over now. I'm glad your taking the time to enlighten me.

Ah.. I didn't know about string.c_str() /cry that could have saved me a few years.

[laserlight]

I don't have a g++ manual.

That can be rectified by consulting the appropriate documentation at the GCC website: GCC online documentation.