Question

I am tried to implement next() PHP function in C. if I have

The different to my implementation is I want to do this work with more one points. For example:

if I have two char * like:

char * a = "ac\0";
char * b = "bd\0";

and I call:

printf("%c", cgetnext(a));
printf("%c", cgetnext(b));
printf("%c", cgetnext(a));
printf("%c", cgetnext(b));

gets an output like: abcd

but I get abab

here is my code:

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

typedef struct 
{
    int pLocation;
    int myindex;
    int lastIndex;
}   POINTERINFORMATION;

int                 __myIndex               = 0;
int                 pointersLocationsLength = 0;
char                * temparr               = NULL;
POINTERINFORMATION  pointersLocations[256];


int 
    plAdd (int p)
    {
        if (pointersLocationsLength >= sizeof(pointersLocations)) {
            return -1;
        } else {
            pointersLocations[pointersLocationsLength].pLocation = p;
            pointersLocations[pointersLocationsLength].lastIndex = 0;
            pointersLocationsLength ++;
            return pointersLocationsLength;
        }
    }

int 
    getPointer (int p, POINTERINFORMATION * out)
    {
        int i;
        for (i = 0; i < pointersLocationsLength; i++)
        {
            if(pointersLocations[pointersLocationsLength].pLocation == p)
            {
                pointersLocations[i].myindex = i;
                *out = pointersLocations[i];
                return 1;
            }
        }

        return 0;
    }

void 
    getPointerIndex(char ** variable, int * val)
    {
        char * buf = malloc(256);
        if(sprintf(buf,"%p", &variable) > 0){
            *val = strtol(buf, NULL, 16 );
        } else {
            *val = -1;
        }
    }

int 
    inArrayOfPointers (int pointer) 
    {
        POINTERINFORMATION pi;
        return getPointer(pointer, &pi);

    }

char 
    cgetnext(char * arr) 
    {
        char * myarr; 
        const size_t size = sizeof(char *) + 1;
        int pof;

        myarr = malloc(size);
        getPointerIndex (&arr, &pof);

        if (inArrayOfPointers(pof)){
            POINTERINFORMATION pi;

            if (getPointer(pof, &pi))
            {
                myarr = (char *)*(int *)pi.pLocation;
                __myIndex = pi.lastIndex;
                ++pointersLocations[pi.myindex].myindex;
            } else {
                return 0;
            }

        } else {

            if (plAdd(pof) == -1) {
                printf(" CANNOT ADD ELEMENT TO ARRAY\n");
                exit(0);
            } else {
                myarr = arr;
                __myIndex = 0;
            }
        }

        if (strlen(myarr) == __myIndex) {
            return 0;
        } else  {
            temparr = malloc(size);
            temparr = strdup(myarr);

            return myarr[__myIndex];
        }
    }`

how to fix this? differents solutions for solve it are very apreciated! Thanks in advance.

Answer 1

If you are specifically interested in char* “arrays”, then a simple solution might be to just increment the pointer. Note that if using dynamically allocated memory, you need to save the original pointer to free it. The same idea could be used for other data types as well.

This is an example of what I mean. cgetnext here just returns the character at the current position in the array and increments pointer (that is passed by address).

char cgetnext( char **p )
{
   assert( p != NULL );
   // check for end of string
   if ( **p == '\0' )
      return '\0';
   return *(*p)++;
}


int main( int argc, char* argv[] )
{
   char *a = "ac";
   char *b = "bd";

   printf( "%c", cgetnext(&a));
   printf( "%c", cgetnext(&b));
   printf( "%c", cgetnext(&a));
   printf( "%c", cgetnext(&b));

}