Sort floating point values from a file (read/write) - c

Question

I am writing a C program that should sort floats (increasingly). The values are saved in a file and then after the sort, the values are saved into the same file. I am using library functions to read and write. I am using radixsort to sort the floats.
This is the code I currently have. Rather than the array being populated with values from the file that I am reading, it is storing 0.000000 for every index. I am not sure where I am going wrong in my implementation.
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <stdlib.h>
void swap(float *a, float *b, size_t n )
{
for ( size_t i = 0; i < n; i++ )
{
float tmp = a[i];
a[i] = b[i];
b[i] = tmp;
}
}
void radixSort(float array[], size_t count)
{
int numZeroes=0;
float tempArr1[count];
float * tempArr2 = tempArr1;
for (uint32_t radix=1;radix;radix<<=1){
uint32_t * intArray = (uint32_t *)array;
int count0=0;
int count1=0;
numZeroes=0;
for (int j=0; j<count; ++j)
numZeroes += !(intArray[j]&radix);
count1=numZeroes;
for (int j=0; j < count; ++j)
if (intArray[j]&radix){
tempArr2[count1]=array[j];
++count1;
}
else{
tempArr2[count0]=array[j];
++count0;
}
swap(tempArr2,array,count);
}
if (numZeroes<count){
memcpy( tempArr2+(count-numZeroes), array, numZeroes*sizeof(float));
for (int d=0,j=count-1;j>=numZeroes;j--,d++)
tempArr2[d]=array[j];
memcpy( array, tempArr2, count * sizeof(float));
}
}
int main(int argc, char *argv[]) {
FILE *fd, *writeFile;
int i = 0;
float number;
int elementnum = 0;
struct stat st;
int fd2;
fd=fopen(argv[1], "r");
fd2 = fileno(fd);
if(fd==NULL){
printf("Error opening file\n");
}
fstat(fd2, &st);
off_t size = st.st_size;
for(int j = 0; j < size/4; j++){
elementnum++;
}
float array[elementnum];
while(fscanf(fd, "%f", &number)==1) {
array[i] = number;
i++;
}
radixSort(array,elementnum);
for(int j = 0; j < elementnum; j++){
printf("%f\n", array[j]);
}
fclose(fd);
writeFile=fopen("argv[1]", "w");
for(int j = 0; j < elementnum; j++){
fprintf(writeFile, "%f\n", array[j]);
}
fclose(writeFile);
return 0;
}

Answer 1

At least these issues:
Code is assuming the size of the text file divided by 4 is the number of float. This is risky and error prone. #agus
Instead of fstat(fd2, &st);, count them
size_t elementnum = 0;
while(fscanf(fd, "%f", &number)==1) {
elementnum++;
}
rewind(fd);
float array[elementnum];
for (i=0; i < elementnum; i++) {
if (fscanf(fd, "%f", &number) != 1) {
puts("We have trouble reading the same on the 2nd pass");
exit(1);
}
array[i] = number;
}
radixSort(array, elementnum);
/ 4 might make sense with a binary file and using fread() to read float.
it is storing 0.000000 for every index
Writing float with "%f" is uninformative with small values. Better to use "%e" or "%g".
#include <float.h>
// fprintf(writeFile, "%f\n", array[j]);
fprintf(writeFile, "%g\n", array[j]);
// or better
fprintf(writeFile, "%.*g\n", FLT_DECIMAL_DIG, array[j]);