Thread: Seg Fault In My Texture Loading Functions

I have two functions, one takes a file name and a pointer to a GLuint. It appears the textures get loaded OK, but I get a segmentation fault in a call to glBindTexture();

Code:

#include "textureloader.h"

bool loadTexture(const char* fname, GLuint *texid, GLuint internalF, GLuint byteF)
{
	SDL_Surface* imgFile;
	if ((imgFile = IMG_Load(fname)) == NULL) //Load Image to an SDL surface
	{
	    return false;
	}
    glPixelStorei(GL_UNPACK_ROW_LENGTH,0);
    glGenTextures(1,texid);
    glBindTexture(GL_TEXTURE_2D,*texid); //Segementation Fault NOT here
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
    glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
    glTexImage2D(GL_TEXTURE_2D,0,internalF,imgFile->w, imgFile->h,0,byteF,GL_UNSIGNED_BYTE,imgFile->pixels);
    SDL_FreeSurface(imgFile);
    return true;
}

bool loadEmUp(char* fname, GLuint *texsToLoad)
{
    std::string texpath;
    int texnum;
    GLuint internalformat, byteformat;
    int texcount = 0;
    std::ifstream texfile (fname);
    if (texfile.is_open())
    {
        texfile >> texnum; //Now holds the number of textures
        texsToLoad = new GLuint[texnum]; //Create room for the new textures
        while (texcount < texnum)
        {
            texfile >> texpath;
            texfile >> internalformat;
            texfile >> byteformat;
            if (!loadTexture(texpath.c_str(), &texsToLoad[texcount], internalformat, byteformat))
            {
                std::cout << "Failed to load image: " << texpath << std::endl;
                return false;
            }
            else std::cout << "Loaded " << texpath << std::endl;
            texcount++;
        }
        texfile.close();
    }
    else return false;
    std::cout << texnum << " Textures Loaded" << std::endl;
    return true;
}

The file with textures names in it is something like this:

Code:

2
media/img1.png 3 3
media/img2.png 3 3

Segmentation fault does not occur in the the loadTexture() function, it's in a different one. Also: GLuint *texsToLoad is declared as a global where the loadEmUp() functions is called from, but it's named myTextures.

In func_one(), myArray is a pointer to an array of ints. So, myArray[0] is *(myArray + 0), i.e., *myArray, which is the array itself. So what you passed to func_two() is the array itself.

In func_two, toChange is now a pointer to the array. *toChange, therefore, is the first element of the array, thus it is changed to 7.

Back to func_one(). myArray[1] is *(myArray + 1), i.e., the next array. However, myArray only points to one array, thus this is a mistake. What you should write is:

Code:

*myArray = new int[2];
func_two(&(*myArray)[0]);
func_two(&(*myArray)[1]);

Better yet, use pass by reference:

Code:

#include <iostream>

void func_two(int& toChange)    //like loadTexture()
{
    toChange = 7;
}

void func_one(int*& myArray)    //like loadEmUp()
{
    myArray = new int[2];
    func_two(myArray[0]);
    func_two(myArray[1]);
}

int main()
{
    int *myArray = 0; // To safely delete[] if new[] is not done.
    func_one(myArray);
    std::cout << myArray[0] << std::endl;
    std::cout << myArray[1] << std::endl;
    delete[] myArray; // Remember to delete[] what you new[] !
}