How to read blocks of float[15] from a binary file???

[delic]

I thought the following would read in blocks of 15 floats from a binary file but after a bunch of correct reads all the output numbers are giberish, numbers like 1E-20 type stuff..

I have to use stdio routines like fread, I have written the same code with fstreams and it works fine. I am missing some stdio quirk or something.. It seems to get hosed when the _cnt variable in the FILE structure becomes < then the size of 15 floats (60).. I believe it has to do with the buffering of the file, which is the system 4096 size.

I have done more debugging.. _cnt gets to a value of 1 then the next fread reads data that is 1516 bytes downstream instead of 60 (note that this is not even a multiple of 60, my block size).. for no reason, I have no seeks or anything in the code..

float CPDATA[15];
do{
fread((char*)CPDATA,sizeof(float)*15, 1, thO->fd);
//outfile read info to a file
outfile<<ftell(thO->fd)<<" ";
for(int i=0;i<15;i++)
outfile<<CPDATA[i]<<" ";
outfile<<endl;

k++;
}while(k<j);

[dumah]

Ok, my C sucks as I have been using C++ for ages (much nicer IMO ;)), so any nasties here, please forgive me. :)

You shoulnd have to look at the members of the FILE struct for something as simple as this, my guess is a problem with your code


#include <stdio.h>
#include <malloc.h>

#define MY_MAX_FLOATS 15

int main(){

FILE *out = 0,*in = 0;//File pointers
float* ptrFloat = 0;//memory I will use to read file
char *szFileName = "Hello.txt";//Name of file
int i;//iterator
float flArray[MY_MAX_FLOATS];//Array I will write to file

for(i = 0;i < MY_MAX_FLOATS;i++)
flArray[i] = i+1 * 1.1;//fill array wilth float info

out = fopen(szFileName,"wb");//open output file
if(!out){
puts("Error opening file");
return 1;
}

fwrite(flArray,sizeof(float)*MY_MAX_FLOATS,1,out);//Write info to file
if(ferror(out)){
puts("Error writting to file");
fclose(out);
return 1;
}

fclose(out);//close output file

//*********************************************************************
// We now have a file with 15 floats that we want to read
//*********************************************************************

in = fopen(szFileName,"rb");//open file to read
if(!in){
puts("Error opening file");
return 1;
}

ptrFloat = malloc(MY_MAX_FLOATS * sizeof(float));//allocate memory for 15 floats
if(!ptrFloat){
puts("Error allocating memory");
fclose(in);
return 1;
}

fread(ptrFloat,sizeof(float)*MY_MAX_FLOATS,1,in);//read all that data
if(ferror(in)){
puts("Error reading file");
fclose(in);
return 1;
}

for(i = 0;i < MY_MAX_FLOATS; ++i){
printf("%.2f\n",ptrFloat[i]);//write to screen
}

fclose(in);//free file
free(flArray);//And memory
return 0;
}

[delic]

Well thanks for the reply.. Yeah it has to do with the porting of the code to windows from unix..

Aggh, I agree c++ is much nicer and that is why this was one of those cases where it is easier to rewrite the code using fstreams. And I did and it worked great..

It had to have been some wierd stdio bug or something because I literally rewrote each line of code with an equivalent line of fstream code and it works great.. So in the end I still dont know the C code doesnt work but I went around the probelm..