Ordering no of strings according to given order - c

Question

If the OrderString is ”dcfbae”, it means d > c > f > b > a > e, unlike the lexicographic(dictionary)
ordering where we have a > b > c > d > e > f.
all are lower case alphabets.
I'm getting SEG FAULT..i know its somewhat related to pointers but i'm unable to figure it out..
here's my code :
#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include<string.h>
#define MAX 1001
int min(int x,int y){
return (x>y)?y:x;
}
int check(char a,char b,char *order){
int i,x,y;
for(i=0;i<strlen(order);i++){
if(a==order[i])
x=i;
if(b==order[i])
y=i;
}
if(x>y)
return 1;
else
return 0;
}
int compare(char *a,char *b,char *order){
int i=0,l1=strlen(a),l2=strlen(b);
for(i=0;i<min(l1,l2);i++){
if(a[i]==b[i])
continue;
else{
if(check(a[i],b[i],order)==1)
return 1;
else
return 0;
}
}
}
void merge(int l,int r,int mid,char **string,char *order){
int size1=mid-l+1;
int size2=r-mid;
char a[size1][MAX],b[size2][MAX];
int i,j,k;
for(i=0;i<size1;i++)
strcpy(a[i],string[l+i]);
for(i=0;i<size2;i++)
strcpy(b[i],string[mid+1+i]);
i=0;
j=0;
k=0;
while(i<size1 && j<size2){
if(compare(a[i],b[j],order)==0){
strcpy(string[k],a[i]);
i++;
}
else{
strcpy(string[k],b[j]);
j++;
}
k++;
}
while(i<size1){
strcpy(string[k],a[i]);
i++;
k++;
}
while(j<size2){
strcpy(string[k],b[j]);
j++;
k++;
}
}
void mergesort(int l,int r,char **string,char *order){
int mid=(l+r)/2;
if(l<r){
mergesort(l,mid,string,order);
mergesort(mid+1,r,string,order);
merge(l,r,mid,string,order);
}
return ;
}
int main(){
char order[MAX];
scanf("%s",order);
int T;
scanf("%d",&T);
char string[T][MAX];
int i;
for(i=0;i<T;i++)
scanf("%s",string[i]);
mergesort(0,T-1,string,order);
for(i=0;i<T;i++)
printf("%s\n",string[i]);
return 0;
}
i'm using mergesort algorithm..
thanks in advance :)

Answer 1

You declare your mergesort() as follows:
void mergesort(int l,int r,char **string,char *order)
But then you invoke it as follows:
mergesort(0,T-1,string,order);
Where string is defined as follows:
char string[X][Y];
So, this is wrong: your mergesort expects a pointer to an array of pointers to char, and you are passing it an array of char.
And if your compiler is not giving you an error, or at least a warning for this, then this means that you are trying to develop software without the bare minimum warnings enabled, or you are using your compiler in some compatibility mode for some paleolithic version of C. Which is a lost cause. So, before fixing anything, before even touching your code again, figure out how to enable all warnings on your compiler, or how to get your compiler to compile for the latest C standard.
To fix this, you could either do what #kkk suggested, which tough might be a bit of work, because you'd have to fix the way your mergesort function works, or you could try to declare your string variable as follows: char** string; Then, you would have to allocate memory for it, with something like this: string = malloc( T * sizeof char* ); and then, right before reading each string, allocate each string like this: string[i] = malloc( (MAX + 1) * sizeof char ); I don't have a C compiler handy, so I can't verify that I got the syntax exactly right, but this should help you get started.

Answer 2

If the purpose is to avoid a crash or segfault avoid warnings first.
by the way char ** and char [][] are not different.
change this
void merge(int l,int r,int mid,char **string,char *order){
to
void merge(int l,int r,int mid,char string[][MAX],char *order){
and this
void mergesort(int l,int r,char **string,char *order){
to
void mergesort(int l,int r,char string[][MAX],char *order){
Now you'll run into not working state

Answer 3

Well I do not Understand your code but at least I can give you a code with no errors and you can check where is the problem in your code.
If you get wrong Answer it happens because you coded wrong.
Here is the code:
#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include<string.h>
#define MAX 1001
int min(int x,int y){
return (x>y)?y:x;
}
int check(char a,char b,char *order){
int i,x=0,y=0;
for(i=0;i<(int)strlen(order);i++){
if(a==order[i])
x=i;
if(b==order[i])
y=i;
}
if(x>y){
return 1;
}else{
return 0;
}
}
int compare(char *a,char *b,char *order){
int i=0,l1=(int)strlen(a),l2=(int)strlen(b);
for(i=0;i<min(l1,l2);i++){
if(a[i]==b[i]){
continue;
}else{
if(check(a[i],b[i],order)==1){
return 1;
}
}
}
return 0;
}
void merge(int l,int r,int mid,char string[][MAX],char *order){
int size1=mid-l+1;
int size2=r-mid;
char a[size1][MAX],b[size2][MAX];
int i,j,k;
for(i=0;i<size1;i++){
strcpy(a[i],string[l+i]);
}
for(i=0;i<size2;i++){
strcpy(b[i],string[mid+1+i]);
}
i=0;
j=0;
k=0;
printf("before :\n");
for(i=0;i<size1+size2;i++)
printf("%s\n",string[i]);
while(i<size1 && j<size2){
if(compare(a[i],b[j],order)==0){
strcpy(string[k],a[i]);
i++;
}else{
strcpy(string[k],b[j]);
j++;
}
k++;
}
while(i<size1){
strcpy(string[k],a[i]);
i++;
k++;
}
while(j<size2){
strcpy(string[k],b[j]);
j++;
k++;
}
}
void mergesort(int l,int r,char string[][MAX],char *order){
int mid=(l+r)/2;
if(l<r){
mergesort(l,mid,string,order);
mergesort(mid+1,r,string,order);
merge(l,r,mid,string,order);
}
}
int main(void){
char order[MAX];
int t,i;
if(scanf("%s",order) != 1){
exit(1);
}
if(scanf("%d",&t) != 1){
exit(1);
}
char string[t][MAX];
for(i=0;i<t;i++)
if(scanf("%s",string[i]) != 1){
exit(1);
}
mergesort(0,t-1,string,order);
return 0;
}
Output:
michi#michi-laptop:~$ ./program
acb
2
cab
bac
before :
cab
bac