C++ Segmentation Fault when loading Image Pixels from Binary File - c++

Question

Doing some C++ for fun and have a problem where when I load an Image after doing some modifications to the image, it gives me segmentation fault. I feel like I'm missing something but I don't know where.
EDIT Here's the code for both the save and load function, (assume that all necessary header files are included):
int Image::save(const char* filename)
{
if(filename == NULL)
{
return 1;
}
///*
ofstream outFile(filename, ios::out | ios::binary);
if (!outFile)
{
return 1;
}
outFile.write(reinterpret_cast<char*>(&cols), sizeof(unsigned int));
outFile.write(reinterpret_cast<char*>(&rows), sizeof(unsigned int));
outFile.write(reinterpret_cast<char*>(pixels), sizeof(uint8_t) * cols * rows);
outFile.close();
return 0;
}
int Image::load(const char* filename)
{
if(filename == NULL)
{
return 1;
}
///*
ifstream inFile(filename, ios::in | ios::binary);
if (!inFile)
{
return 1;
}
**//feels like the segmentation fault is happening here**
inFile.read(reinterpret_cast<char*>(&cols), sizeof(unsigned int));
inFile.read(reinterpret_cast<char*>(&rows), sizeof(unsigned int));
inFile.read(reinterpret_cast<char*>(pixels), sizeof(uint8_t) * cols * rows);
inFile.close();
return 0;
}
EDIT
Here's the header file that I am working with:
class Image {
public:
unsigned int cols;
unsigned int rows;
uint8_t* pixels;
...
/* Saves the image in the file filename. In a format that can be
loaded by load(). Returns 0 on success, else a non-zero error
code. */
int save( const char* filename );
/* Load an image from the file filename, replacing the current
image size and data. The file is in a format that was saved by
save(). Returns 0 success, else a non-zero error code . */
int load( const char* filename );
};

Answer 1

You're moving the file pointer to the end of the file before trying to read it when you open it with ios::ate. You want to read from the beginning of the file, so ios::ate should be removed.
Also you are reading in a loop, and not writing in a loop. Your while should be an if, or just removed.
Also read does not adjust your pointer (or shouldn't...see my next point), but merely reads data into where you are pointing to. So the NULL check (if pixels==NULL) is nonsensical.
Also, you shouldn't be using the address-of operator (&) for pixels. pixels is already a pointer and both your read and write of this variable should have the & removed, like so:
inFile.read(reinterpret_cast<char*>(pixels), sizeof(uint8_t) * cols * rows);
You may find this helpful:
http://boredzo.org/pointers/
edit:
inFile.read(reinterpret_cast<char*>(&cols), sizeof(unsigned int));
inFile.read(reinterpret_cast<char*>(&rows), sizeof(unsigned int));
resize(cols, rows, 0);
inFile.read(reinterpret_cast<char*>(pixels), sizeof(uint8_t) * cols * rows);
Your resize() needs to make sure the pointer isn't NULL before trying to delete it, and you probably should make fill() a separate function.
But at least do
int Image::resize(unsigned int width, unsigned int height, uint8_t fillcolor)
{
if (pixels != NULL)
delete[] pixels;
...

Answer 2

In addition to #zzxyz's answer, you may be running into a problem with byte order. When you read cols and rows, c++ might order the bytes in integers from least significant to most significant (little endian), while the file could order the bytes from most significant to least significant (big endian), for example (see more here). This could give you values of cols and rows wildly different from what you expect, and reading cols * rows bytes could make inFile try to read far beyond the length of the file. I recommend checking or printing the values of cols and rows and making sure they line up with what you expect; if not, you'll have to reverse the order of the bytes in the integers.