sorting file

[meabed]

hello,
i want to sort a file and i don't know how to put the data from a certain field of the file in a vector, sort it and then put it back in the file.
here's what i've done.

FILE *file; 
struct catalog{char 1rst_field,2nd_field,3rd_field}name,v[100]; 

//here i put the data in the file 

typedef int(*fcmp)(const void*,const void*) 
cmp1rst_field(catalog a1,catalog a2) 
{return a1.1rst_field-a2.1rst_field} 
int a[100],n=100,i; 

void sort() 
{ 
while(!feof(file)) 

//here i'd have to put the data from 1rst_field in a[i];i++; 

qsort(&a[0],n,sizeof (int),(fcmp)cmp1rst_field)
}

i'd appreciate any help with this sorting algorithm or another that would be simpler.thank you.