I have a C struct declared as below (just a simple example):
typedef struct
{
float score;
char* name;
}
person;
So, along the program, I changed the value of the person's score (i gave them an initial value). So, i plan to put all of the scores inside a vector and sort them. Then, I would like to print a list of the name of all the persons, starting from biggest score to smallest score. Any idea on this last part? I'm not sure how to code it. Thanks.
Similar to the C++ approach above, there is a library function in the C standard library called qsort. It is based upon a comparision function, that creates the ordering on the array members.
For your case a minimal example could look like this:
#include <stdlib.h>
#include <stdio.h>
// Definitiion of a person
typedef struct person
{
float score;
char *name;
} person;
// Some small epsilon
#define EPSILON 1.0e-3f
// Comaprision function. Returns <0 for a<b =0 for a=b and >0 for a>b
static int compare_people( const void *a, const void *b )
{
// Cast to the correct pointer type
const person *p1 = (const person*) a;
const person *p2 = (const person*) b;
// There are different ways of comparing floats to each other. In this case we use |a - b| < epsilon for some small epsilon
float difference = p2->score - p1->score;
if( difference <= -EPSILON )
{
return -1;
}
else if( difference >= +EPSILON )
{
return +1;
}
return 0;
}
int main()
{
// Initialize list of people
size_t num_people = 5;
person people[num_people];
people[0].score = 0.3f;
people[0].name = "Homer";
people[1].score = 1.4f;
people[1].name = "Marge";
people[2].score = 0.02f;
people[2].name = "Bart";
people[3].score = 13.2f;
people[3].name = "Lisa";
people[4].score = 1.0f;
people[4].name = "Maggie";
// Print unsorted
printf( "Unsorted:\n" );
for( size_t i = 0; i < num_people; ++i )
{
printf( " %s - %2.2f\n", people[i].name, people[i].score );
}
printf( "\n" );
// Sort
qsort( people, num_people, sizeof(person), &compare_people );
// Print sorted
printf( "Sorted:\n" ) ;
for( size_t i = 0; i < num_people; ++i )
{
printf( " %s - %2.2f\n", people[i].name, people[i].score );
}
printf( "\n" );
// Done
return EXIT_SUCCESS;
}
Note the comment about comparing floating point values.
If you are using Linux, you can investigate system calls and functions of the C standard library by looking up the corresponding man page, e.g.
man qsort
For example you ll have
vector<person> vec;
Now you want sort this using sort from STL
You first must create method for operator " < "
bool operator<(const person& a, const person& b){
return a.score<b.score;
}
I hope this helps you I m sorry for my bad grammar :)
Example of usage
sort(vec.begin(),vec.end(),[](const person& a, const person&b){return b<a});
Now your vector of person will be sorted upside - down order.
