Sorting strings in C

So I got the sorting program to work when I set the array without any numbers. However when reading from a file which has numbers before the word it is not behaving the way I want it to.

Code:

---

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
 


int cmpstr(void* v1, void* v2)
{
   
    char *a1 = *(char**)v1;
    char *a2 = *(char**)v2;
    return strcmp(a1, a2);
}
 
// function for comparing two strings


void swap(void* v1, void* v2, int size)
{
   
    char buffer[size];
 
   
    memcpy(buffer, v1, size);
    memcpy(v1, v2, size);
    memcpy(v2, buffer, size);
}
 


void _qsort(void* v, int size, int left, int right,
                      int (*comp)(void*, void*))
{
    void *vt, *v3;
    int i, last, mid = (left + right) / 2;
    if (left >= right)
        return;
 
    // casting void* to char* so that operations 
    // can be done.
    void* vl = (char*)(v + (left * size));
    void* vr = (char*)(v + (mid * size));
    swap(vl, vr, size);
    last = left;
    for (i = left + 1; i <= right; i++) {
 
       
        vt = (char*)(v + (i * size));
        if ((*comp)(vl, vt) > 0) {
            ++last;
            v3 = (char*)(v + (last * size));
            swap(vt, v3, size);
        }
    }
    v3 = (char*)(v + (last * size));
    swap(vl, v3, size);
    _qsort(v, size, left, last - 1, comp);
    _qsort(v, size, last + 1, right, comp);
}
 
int main()
{
   
    char* a[] = {"bbc", "xcd", "ede", "def",
            "afg", "hello", "hmmm", "okay", "how", "welcome" };
 
   
    _qsort(a, sizeof(char*), 0, 8, (int (*)(void*, void*))(cmpstr));
   
    for (int i = 0; i < 10; i++)
        printf("%s ", a[i]);
    printf("\n");
 
   
}

---

The desired output for the input is shown.
Attachment 16275
Attachment 16276

Well yeah, you need to show how you're reading from the file, how you're parsing the data and how you're constructing the array to be sorted.

@salem I made a few tweaks. Now it comes to segmentation fault.

Code:

---

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
 
 
int cmpstr(void* v1, void* v2)
{ 
    char *a1 = *(char**)v1;
    char *a2 = *(char**)v2;
    return strcmp(a1, a2);
}
 

 

void swap(void* v1, void* v2, int size)
{
   
    char buffer[size];
 
   
    memcpy(buffer, v1, size);
    memcpy(v1, v2, size);
    memcpy(v2, buffer, size);
}
 

void char_sort(void* v, char size, char left, char right,
                      char (*comp)(void*, void*))
{
    void *vt, *v3;
    int i, last, mid = (left + right) / 2;
    if (left >= right)
        return;
 
   
    void* vl = (char*)(v + (left * size));
    void* vr = (char*)(v + (mid * size));
    swap(vl, vr, size);
    last = left;
    for (i = left + 1; i <= right; i++) {
 
       
        vt = (char*)(v + (i * size));
        if ((*comp)(vl, vt) > 0) {
            ++last;
            v3 = (char*)(v + (last * size));
            swap(vt, v3, size);
        }
    }
    v3 = (char*)(v + (last * size));
    swap(vl, v3, size);
    char_sort(v, size, left, last - 1, comp);
    char_sort(v, size, last + 1, right, comp);
}
 
int main()
{
    char a[10];
    FILE *in, *out;
    in = fopen("alphabetic_sort.dat", "r");
    out = fopen("sort.out", "w");
   
    while (1)
    {
        fscanf(in, "%d", &a);
        char_sort(a, sizeof(char*), 0, 10, (char (*)(void*, void*))(cmpstr));
   
        int i;
        for (i = 0; i < 9; i++)
        fprintf(out, "%s \n", a[i]);
       
    }
   
   
 
  return 0; 
}


---

Post it again, this time without the awful fonts from your IDE.

Sorry @salem. Posting it again

Code:

---

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
 
 
int cmpstr(void* v1, void* v2)
{ 
    char *a1 = *(char**)v1;
    char *a2 = *(char**)v2;
    return strcmp(a1, a2);
}
 


 


void swap(void* v1, void* v2, int size)
{
   
    char buffer[size];
 
   
    memcpy(buffer, v1, size);
    memcpy(v1, v2, size);
    memcpy(v2, buffer, size);
}
 


void char_sort(void* v, char size, char left, char right,
                      char (*comp)(void*, void*))
{
    void *vt, *v3;
    int i, last, mid = (left + right) / 2;
    if (left >= right)
        return;
 
   
    void* vl = (char*)(v + (left * size));
    void* vr = (char*)(v + (mid * size));
    swap(vl, vr, size);
    last = left;
    for (i = left + 1; i <= right; i++) {
 
       
        vt = (char*)(v + (i * size));
        if ((*comp)(vl, vt) > 0) {
            ++last;
            v3 = (char*)(v + (last * size));
            swap(vt, v3, size);
        }
    }
    v3 = (char*)(v + (last * size));
    swap(vl, v3, size);
    char_sort(v, size, left, last - 1, comp);
    char_sort(v, size, last + 1, right, comp);
}
 
int main()
{
    char a[10];
    FILE *in, *out;
    in = fopen("alphabetic_sort.dat", "r");
    out = fopen("sort.out", "w");
   
    while (1)
    {
        fscanf(in, "%d", &a);
        char_sort(a, sizeof(char*), 0, 10, (char (*)(void*, void*))(cmpstr));
   
        int i;
        for (i = 0; i < 9; i++)
        fprintf(out, "%s \n", a[i]);
       
    }
   
   
 
  return 0; 
}

---

Why are you saving the integer inside the char array? Why are you passing "sizeof(char*)" as the size?

Btw, you don't want to use "char" for the types of size and left/right. "int" would be much better.

Also btw, the way I see it, the number in front of each line is the amount of characters you should allocate on the heap(malloc/free etc), inside which you'd read the string.

> However when reading from a file which has numbers before the word it is not behaving the way I want it to.
This would suggest your input should be

Code:

---

int a;
char b[100];
fscanf(in, "%d %s", &a, b);

---

Also, before you do any file reading at all, make sure this works.

Code:

---

    char a[10] = "qawsedrftg";
    char_sort(a, sizeof(char), 0, 10, (char (*)(void*, void*))(cmpstr));
    for (i = 0; i < 9; i++)
        printf("%d = %c\n", i, a[i] );

---