Extracting 2 byte decimal values from a binary file

[cg9289]

Hi, I am trying to extract to byte decimal values from a binary file for anaylsis.

my current code

#include "../../std_lib_facilities.h"


using namespace std;

int main()
{
    vector<double>xCount;
    vector<double>yCount;
    vector<double>header;
    vector<double>sample;
    string searchPattern;
    double max;
    double min;
    double keyMax;
    double finalTime;
    char * memblock =0;
    int size;

    ifstream file("c:\\WAV\\BEandDAexp4_22post.wav",ios::ate|ios::binary);
    
    if(file.is_open()) 
    {
       int data;
       cout<< "Starting Stream" << endl;

       size = (int)file.tellg();                // Use's eof operator to see how large the file is.
       data = (size-44);
       memblock = new char[data];          
       file.seekg(44,ios::beg);
       file.read(memblock, data);              // Reads file using 'size' as the itterator of where to stop, set by ios::ate
       
       max =0;
       min =0;
       int conv = 0;
       for( int i =0; i<data ; ++i )                //For loop that will store the values of the binary vector as double's
        {                                            //by casting and storing in private data member yCount 
            conv = static_cast<double>(memblock[i]);
            yCount.push_back(conv);

            if(conv>max)
            {                         // starting with zero and comparing to our string 
                max = conv;              // Finds new max value and time associated with it. 
            }
            else if (conv<min)
            {                          // starting with zero and comparing to our string finds largest negative value
                min = conv;
            }
        }

        
        delete []memblock;
    }
    for(int i=0; i<200; i+=2)
    {
        cout<<static_cast<int>((yCount[i]) << "  ";
    }

    file.close();

Out puts the correct single byte decimal values.

I need them in two byte pieces because the sample sizes are two bytes but, the problem is,

.read() that I am using takes a char * as it's argument.

Thanks in advance

Steave

[Philip Nicoletti]

I am confused. You say 2 byte decimal, but you seem to want
a double (which is probably 8 bytes). Plus "decimal" is not a C++
type. Do you mean a short ? unsigned short ? both of which
might be 2 bytes in size.

If so, the basic algorithm would be:

short value;  // unsigned short ???

while ( file.read( (char *)&value , sizeof(short) ) )
{
   // do something with value
}

[cg9289]

OK I am trying to implement the code, and I am probablly doing something naive.

    ifstream file("c:\\WAV\\BEandDAexp4_22post.wav",ios::ate|ios::binary);
    
    if(file.is_open()) 
    {
        short value =1;  // unsigned short ???

        cout<< "1" << endl;
        while ( file.read( (char *)&value , sizeof(short) ) )
        {
            sample.push_back(value);
        }
    }

    for(int a = 0; a<200 ; ++a)
    {
        cout<< sample[a] << " ";
    }


}

It is throwning an error that says vector subscript out of range

I need to pushback the values of the binary file into a vector to anazlye the data.

Thanks

steave

[Philip Nicoletti]

1) in your open statement you have : ios::ate ... so the stream position is set to the
end of the file. Therefore, no values will be read.

2) in your for statement at the end, you are using : 200 ... it should be sample.size()