• Create Account

# Writing to a file

Old topic!

Guest, the last post of this topic is over 60 days old and at this point you may not reply in this topic. If you wish to continue this conversation start a new topic.

3 replies to this topic

### #1Azenris  Members   -  Reputation: 139

Like
0Likes
Like

Posted 18 June 2012 - 10:36 AM

Hi, i have this function where I must be misunderstanding something because it is not as expected and I cannot figure out whats going on. Hoping for some help

std::string CreateTempConvertedGfx(const std::string & name, const std::string & filename)
{
std::string handle = CreateHandle(name);
std::string tempFileName = "temps/" + handle + ".tmp";

TargaImage image;

{
std::cout << "ERROR: Could not load targa image: " << filename << std::endl;
while(1);
}

int frames = 1;
int frameDelay = 10;
int frameWidth = 16;
int frameHeight = 16;

frames = image.getWidth() / frameWidth;

GRAPHIC_DATA gfxData;

strcpy(gfxData.m_handle, handle.c_str());

gfxData.m_frames = frames;
gfxData.m_frameDelay = frameDelay;
gfxData.m_frameWidth = frameWidth;
gfxData.m_frameHeight = frameHeight;

gfxData.m_textureWidth = image.getWidth();
gfxData.m_textureHeight = image.getHeight();
gfxData.m_textureSize = image.getSize();

std::ofstream dstFile(tempFileName);

if (dstFile.is_open() == false)
{
std::cout << "ERROR: Could not open dst: " << tempFileName << std::endl;
while(1);
}

long startp = dstFile.tellp();

dstFile.write((char *)&gfxData, sizeof(GRAPHIC_DATA));				   // temp - THIS IS WRITING 61 BYTES WHEN GRAPHIC_DATA is 60 ?!

// temp
// these should be equal, and they are for Potion, the one with a gdf file
// if you remove the gdf file it stops working and any you add one too
// start to work
// why does having a gdf file making it work and not having one break it
long tellpp = dstFile.tellp();
if (tellpp != sizeof(GRAPHIC_DATA))
{
std::cout << "ERROR: " << tempFileName << " [" << tellpp << " / " << sizeof(GRAPHIC_DATA) << "] : " << startp << std::endl;
while(1);
}
// end temp

dstFile.write((char *)image.getImageData(), image.getSize());

dstFile.close();

return tempFileName;
}


The problem is, the line
dstFile.write((char *)&gfxData, sizeof(GRAPHIC_DATA));
After calling this I check the the position with tellp and it ends up 1 position ahead of where it should be (i think).

The weird thing is, this write only goes 1 position past IF I have a .gdf file (just a basic file with some info).

The output ill get is
ERROR: temps/Attribute_Damage.tmp [61/60] : 0

And this error is for all files where ReadGDFFile doesnt open anything. Here is the source to that incase

void ReadGDFFile(const std::string & filename, int & frames, int & frameDelay, int & frameWidth, int & frameHeight)
{
std::string gdfFilename = filename;
size_t end = gdfFilename.find_last_of(".");

if (end == std::string::npos)
{
std::cout << "ERROR: Invalid file name" << std::endl;
while(1);
}

gdfFilename = gdfFilename.substr(0, end + 1) + "gdf";

std::ifstream gdfFile(gdfFilename);

if (gdfFile.is_open())
{
std::string option;

while (gdfFile.eof() == false)
{
gdfFile >> option;

if (option == "frameDelay")
{
gdfFile >> frameDelay;
}
else if (option == "frameWidth")
{
gdfFile >> frameWidth;
}
else if (option == "frameHeight")
{
gdfFile >> frameHeight;
}
else
{
std::cout << "Unknown GDF attribute name: " << option;
while(1);
}
}

gdfFile.close();
}
}


const int MAX_GFX_NAME = 32;

#pragma pack(push, 1)

struct GRAPHIC_DATA
{
char m_handle[MAX_GFX_NAME];
int m_frames;
int m_frameDelay;
int m_frameWidth;
int m_frameHeight;
int m_textureWidth;
int m_textureHeight;
int m_textureSize;
};

#pragma pack(pop)


The thing is Im not sure how anything changes how much data is written. sizeof(GRAPHIC_DATA) should always be the same.

To test, compile, then drag and drop the "files" folder onto the exe in the debug folder.

Thanks for any help.

### #2e‍dd  Members   -  Reputation: 2109

Like
1Likes
Like

Posted 18 June 2012 - 12:47 PM

Hi, i have this function where I must be misunderstanding something because it is not as expected and I cannot figure out whats going on. Hoping for some help

std::string CreateTempConvertedGfx(const std::string & name, const std::string & filename)
{
std::string handle = CreateHandle(name);
std::string tempFileName = "temps/" + handle + ".tmp";

TargaImage image;

{
std::cout << "ERROR: Could not load targa image: " << filename << std::endl;
while(1);
}


while(1) ?

	int frames = 1;
int frameDelay = 10;
int frameWidth = 16;
int frameHeight = 16;

frames = image.getWidth() / frameWidth;

GRAPHIC_DATA gfxData;

strcpy(gfxData.m_handle, handle.c_str());


This strcpy call is susceptible to overflow. You should at least make sure handle.size() is strictly less than MAX_GFX_NAME before making the call.

	gfxData.m_frames = frames;
gfxData.m_frameDelay = frameDelay;
gfxData.m_frameWidth = frameWidth;
gfxData.m_frameHeight = frameHeight;

gfxData.m_textureWidth = image.getWidth();
gfxData.m_textureHeight = image.getHeight();
gfxData.m_textureSize = image.getSize();

std::ofstream dstFile(tempFileName);


You probably want to pass std::ios::binary as a second argument to std::ofstream's constructor.

	if (dstFile.is_open() == false)
{
std::cout << "ERROR: Could not open dst: " << tempFileName << std::endl;
while(1);
}

long startp = dstFile.tellp();

dstFile.write((char *)&gfxData, sizeof(GRAPHIC_DATA));				   // temp - THIS IS WRITING 61 BYTES WHEN GRAPHIC_DATA is 60 ?!


I see you took care of padding, but you may want to consider endianness if this format is supposed to be portable, if you haven't already.

	// temp
// these should be equal, and they are for Potion, the one with a gdf file
// if you remove the gdf file it stops working and any you add one too
// start to work
// why does having a gdf file making it work and not having one break it
long tellpp = dstFile.tellp();
if (tellpp != sizeof(GRAPHIC_DATA))


Presumably you mean to check (tellpp - startp) against the sizeof GRAPHIC_DATA? Though I honestly doubt it matters in this case.

	[...]

dstFile.close();


FYI, the destructor of std::ofstream closes the file for you.

And this error is for all files where ReadGDFFile doesnt open anything. Here is the source to that incase

void ReadGDFFile(const std::string & filename, int & frames, int & frameDelay, int & frameWidth, int & frameHeight)
{
std::string gdfFilename = filename;
size_t end = gdfFilename.find_last_of(".");

if (end == std::string::npos)
{
std::cout << "ERROR: Invalid file name" << std::endl;
while(1);
}

gdfFilename = gdfFilename.substr(0, end + 1) + "gdf";


I don't think "end + 1" is correct.

This is possibly a good time to get to know your debugger a little better.

Edited by e‍dd, 18 June 2012 - 12:50 PM.

### #3Azenris  Members   -  Reputation: 139

Like
0Likes
Like

Posted 18 June 2012 - 01:48 PM

The while(1); just creates an infinite loop, essentially halting the program displaying the last error message.

The handle is checked before using strcpy (however it was done in the CreateHandle function I didn't give you the source on in the post).

I'll try the std::ios::binary as a second parameter, ty for the suggestion.

II thought the (end + 1) would return the position past the . (i.e. the extension)
Ill double check it though.

EDIT:

Not treating the file as binary was the problem, THANKS!

Edited by Azenris, 18 June 2012 - 01:51 PM.

### #4e‍dd  Members   -  Reputation: 2109

Like
0Likes
Like

Posted 18 June 2012 - 02:06 PM

II thought the (end + 1) would return the position past the . (i.e. the extension)

Ah yes my mistake, I misunderstood your intention there. Apologies for that.

Not treating the file as binary was the problem, THANKS!