A pointer to a character pointer array... can't pass

I was working on another thread and here's what I came up with:

Code:

---

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

typedef char** char1;
typedef char1 *cptr;

void str_swap(char** str1, char** str2);
void bubble_sort(cptr array,int length)
{
        int i, j,s;
        bool flag = 1; 
        char* tmp;     
        int arrayLength = length;
        for(i = 0; (i < arrayLength) && flag; i++)
        {
                flag = 0;
                for (j=0; j < (arrayLength -1); j++)
                {
                        s = strcmp(*array[j+1],*array[j]);
                        if(s>0)//string 2 is greater
                        {
                                str_swap(array[j+1],array[j]);
                        }
                }
        }
}


int main()
{
        char* str1= "Alfred";
        char* str2 = "Albert";
        char* strs[] = {str1,str2,"Linux","Penguin","Lorraine","Lucas"};
        int len = 6;
        for(int j=0;j<len;j++)
                printf("%s ",strs[j]);
        printf("\n");
        bubble_sort(&strs,len);
        for(j=0;j<len;j++)
                printf("%s ",strs[j]);
        printf("\n");
        return 0;
}

void str_swap(char** str1, char** str2)
{
        char* tmp;
        tmp = *str1;
        *str1 = *str2;
        *str2=tmp;
}

---

but it says cannot convert char(*)(*)[6] to char***
I can't understand why it can't convert it. And do you know of a way I can pass the array of strings into the function and be able to MODIFY that array?

-LC

Stop using typedefs. That's probably your problem. Personally I never use them for just this sort of reason. Typedefs create a new data type, as such, you get wierd conversion problems when mixing them with their non-typedef equivalents.

Just use #define. In C I can really don't see the need to ever use typedefs when you can just #define them. With #define you get the same effect, but it avoids all the type conversion issues since it's simple preprocessor text subsitution.

Quzah.

Nothing wrong with typedefs :)

bubble_sort(&strs,len);
Type is char(*)(*)[6]

bubble_sort(strs,len);
Type is char ***

In both cases, you're passing a pointer to the start of the array, but the TYPE of the pointer is different.

> Just use #define.
Renaming types using #define is a really bad idea

Example

Code:

---

#define int_ptr  int *
int_ptr a_ptr, b_ptr;

---

b_ptr is really an int, not in int*, which casual reading of the code would suggest. If you used a typedef, this would not happen.

@quzah:

Years ago, I had a long, but very interesting discussion with someone (cannot remember who, unfortunately) in this forum. The question was: "Does a typedef create a new type or not?"

The answer is: No, a typedef does not create a new type. It is just an alias. See K&R A.8.9. ;-)

My personal opinion is: Typedefs are okay as long as they help you to simplify a problem. However, do not use them too much. A bad example is the Win32 API, I think.

Regards,
R.

typedefs have a purpose, if they didn't and they were bad, they would be removed from the standard.

who would want to type
char*** cptrptrptr;
many times for each one you define?
it's easier to just
typedef char*** char2;
char2 cptrptrptr;
and it helps you avoid some confusion.

in my opinion, #define is VERY BAD to use for that instance.

and another thing, I only used typedef because I was messing around trying to figure out how I could get it to work.

now it crashes with an access violation (out of bounds I guess)

the new code (LOL):

Code:

---

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

typedef char** char1;
typedef char1 *cptr;

void str_swap(char** str1, char** str2);
void bubble_sort(cptr array,int length)
{
        int i, j,s;
        bool flag = 1; 
        char* tmp;     
        int arrayLength = length;
        for(i = 0; (i < arrayLength) && flag; i++)
        {
                flag = 0;
                for (j=0; j < (arrayLength -1); j++)
                {
                        s = strcmp(*array[j+1],*array[j]);
                        if(s>0)//string 2 is greater
                        {
                                str_swap(array[j+1],array[j]);
                        }
                }
        }
}


int main()
{
        char* str1= "Alfred";
        char* str2 = "Albert";
        char* strs[] = {str1,str2,"Linux","Penguin","Lorraine","Lucas"};
        int len = 6;
        for(int j=0;j<len;j++)
                printf("%s ",strs[j]);
        printf("\n");
        bubble_sort((cptr)&strs,len);
        for(j=0;j<len;j++)
                printf("%s ",strs[j]);
        printf("\n");
        return 0;
}

void str_swap(char** str1, char** str2)
{
        char* tmp;
        tmp = *str1;
        *str1 = *str2;
        *str2=tmp;
}

---

any ideas?

-LC

Here's your code, working, minus the typedefs.

Code:

---

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

typedef int bool;

void        str_swap(char **str1, char **str2);
void bubble_sort(char *array[], int length)
{
  int  i, j, s;
  bool  flag = 1;
  int  arrayLength = length;
  for (i = 0; (i < arrayLength) && flag; i++)
  {
    flag = 0;
    for (j = 0; j < (arrayLength - 1); j++)
    {
      s = strcmp(array[j + 1], array[j]);
      if (s < 0)  //string 2 is greater
      {
        flag = 1;
        str_swap(&array[j + 1], &array[j]);
      }
    }
  }
}

int main(void)
{
  char  *strs[] = { "Alfred", "Albert", "Linux", "Penguin", "Lorraine", "Lucas" };
  int  j, len = 6;
  for (j = 0; j < len; j++) printf("%s ", strs[j]);
  printf("\n");
  bubble_sort(strs, len);
  for (j = 0; j < len; j++) printf("%s ", strs[j]);
  printf("\n");
  return(0);
}

void str_swap(char **str1, char **str2)
{
  char  *tmp;
  tmp = *str1;
  *str1 = *str2;
  *str2 = tmp;
}

---

To add your typedefs back in, simply go through and replace the relevant bits. But you two typedefs are definately bad style imo.

yeah thanks, I don't like tyepdefs that much, I RARELY use them, but I thought I could 'trick' my compiler into accepting it. hehe bad style.

But for all intended purposes it can be good in some cases.

-LC

Quote:

---

Originally posted by Lynux-Penguin
typedefs have a purpose, if they didn't and they were bad, they would be removed from the standard.

---

If that's so, what about gets()?
1) It is bad,
2) hasn't had it's definition fixed, and
3) is still in the standard.
;) ;) ;)

>char2 cptrptrptr;
>and it helps you avoid some confusion.

[opinion type=mine]
...Unless you are the poor SOB that comes across a char2 in some code you are maintaining. Then you get to track down its definition, which may be in some header file somewhere. But a char*** would mean the same thing and require no detective work. And you wouldn't even need to use an ugly name like cptrptrptr to know what it is.

I think the best use for typedefs is with function pointers. About the only other place I care to use them is for platform-specific exact-sized integers. Anything else (structs, unions, enums), in my opinion, hides information from the programmer.(!)
[/opinion]

Quote:

---

Originally posted by Salem
> Just use #define.
Renaming types using #define is a really bad idea

Example

Code:

---

#define int_ptr  int *
int_ptr a_ptr, b_ptr;

---

b_ptr is really an int, not in int*, which casual reading of the code would suggest. If you used a typedef, this would not happen.

---

Yeah but who on earth typedefs pointers? Not me. Ug. I hate that with a passion. If I want a pointer, I'll add a little * next to the variable. I hate variable types which are defined as pointers. It bugs the hell out of me. Because then in the middle of the code you see something like:

Code:

---

mytype foo;

foo->bar = blah;

---

And my brain says, "No, don't do that!, there's no little star!" ;)

Pet peeve of mine. I hate defined pointer types.

[edit=Just read Dave's post]
Couldn't agree more. I hate poinder definitions!
[/edit]

Quzah.