Visual Studio Release and Debug difference - c++

Question

I'm writing a code in which I read and image and process it and get a Mat of double/float. I'm saving it to a file and later on, I'm reading it from that file.
When I use double, the space it requires is 8MB for 1Kx1K image, when I use float it is 4MB. So I want to use float.
Here is my code and output:
Mat data = readFloatFile("file_location");
cout << data.at<float>(0,0) << " " << data.at<double>(0,0);
When I run this code in the DEBUG mode, the print out for float is -0 and double gives exception namely assertion failed. But when I use RELEASE mode the print out for float is -0 and 0.832 for double which is true value.
My question is why I cant get output when I use data.at<float>(0,0) and why I don't get exception when I use data.at<double>(0,0) in RELEASE mode which is supposed to be the case?
EDIT: Here is my code which writes and reads
void writeNoiseFloat(string imageName,string fingerprintname) throw(){
Mat noise = getNoise(imageName);
FILE* fp = fopen(fingerprintname.c_str(),"wb");
if (!fp){
cout << "not found ";
perror("fopen");
}
float *buffer = new float[noise.cols];
for(int i=0;i<noise.rows;++i){
for(int j=0;j<noise.cols;++j)
buffer[j]=noise.at<float>(i,j);
fwrite(buffer,sizeof(float),noise.cols,fp);
}
fclose(fp);
free(buffer);
}
void readNoiseFloat(string fpath,Mat& data){
clock_t start = clock();
cout << fpath << endl;
FILE* fp = fopen(fpath.c_str(),"rb");
if (!fp)perror("fopen");
int size = 1024;
data.create(size,size,CV_32F);
float* buffer= new float[size];
for(int i=0;i<size;++i) {
fread(buffer,sizeof(float),size,fp);
for(int j=0;j<size;++j){
data.at<float>(i,j)=buffer[j];
cout << data.at<float>(i,j) << " " ;
cout << data.at<double>(i,j);
}
}
fclose(fp);
}
Thanks in advance,

Answer 1

The first of all, you can not use the float and double in one cv::Mat as storage itself is only array of bytes. Size of this array will be different for matrix of float and matrix of double.
So, you have to decide what you are using.
Essentially, data.at<type>(x,y) is equivalent to (type*)data_ptr[x][y] (note this is not exact code, its purpose is to show what is happening)
EDIT:
On the basis of code you added you are creating matrix of CV_32F this means that you must use float to write and read and element. Using of double causes reinterpretation of value and will definitely give you an incorrect result.
Regarding to assertion, I am sure that inside the cv::MAT::at<class T> there is a kind of following code:
assert(sizeof<T>==this.getDepth());
Usually asserts are compiled only in DEBUG mode, so that's why you do not give this error in RELEASE.
EDIT2:
Not regarding to issue, but never use free() with new or delete with malloc(). The result can be a hardly debugging issue.
So please use delete[] for buffer.

Answer 2

Difference between debug & release:
There's a bug in your code. It just doesn't show up in Release mode. That is what the debugger is for. Debugger tells you if there's any bug/issue with the code, Release just runs through it...
Also the compiler optimizes your code to run faster and is therefore smaller, the debugger uses more size on your HD because you can actually DEBUG it.
Release initializes your un-initialized variables to 0. This may vary on different compilers.