Retrieving a contain of an Array using pointer

[maxou2013]

Hi,

I was struggling the last 2 days with this C script supposing to open a list of strings (input as fopen(argv[1])and allowing to access to any element of the list. I created an array *gcm[10000] and a pointer *(*gcm_ptr[10000] = &gcm. However, when I try to list whatever n[i], it always gives me the last entry. Thanks in advance for any help.

Max

[maxou2013]

HERE IS THE SOURCE CODE I USED.

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

#define NJFD 3059

main(int argc, char **argv){

FILE *fict;

unsigned short int *data_tab;

char line[1024];
char *cp;
char *n[10000];
char *(*n_ptr)[10000] = &n;

int m,i,quit;




/****** Open files and initialize ******/
if (argc != 2) {
printf("\n command line: <List File> \n");
exit(1);
}

if ( (fict = fopen(argv[1],"r")) == NULL ) {
printf("\n Cannot OPEN TAB file 1\n");
exit(1);
}


data_tab = (unsigned short int *)calloc(NJFD, sizeof(unsigned short int));
if (data_tab == NULL) {
printf("\n Not enough memory for tab data short int array \n");
exit(1);
}

m = 0;
quit = 0;
if(fict != NULL)
{
while((fgets(line, 1024, fict)) && (quit == 0))
{
cp = line;
while((*cp != '\0') && (quit == 0))
{
if((m < 10000))
{
n[m] = cp;
while((*cp != ',') && (*cp != '\0')){
cp++;
}
if(*cp == ',') cp++;

} /* end if */
else
{
quit = 1;
fprintf(stderr, "Error: Rows has exceeded 10000. Exiting program.\n");
} /*end else */

} /* end while ((*cp */
m++;
} /* end while ((fgets */

fclose(fict);

} /*end if (fict */
else
{
fprintf(stderr, "Error: Unable to open textfile.\n");
}

for (i = 0; i < m; i++) printf("List %d: %s\n",i+1, (*n_ptr)[i]);

if (data_tab != NULL) free(data_tab);

}

[weaknessforcats]

*gcm[10000] and a pointer *(*gcm_ptr[10000] = &gcm.

gcm is an array of 1000 pointers.
gcm_ptr is a pointer to an array of 1000 pointers.

Where are the strings exactly?

[maxou2013]

The strings are input from the (fict = fopen(argv[1],"r"); please, see the script above

[weaknessforcats]

fict is a FILE pointer. A FILE is not an array of strings

You have to read the string into an array like line[1024].

Then you need to allocate a new array of 1024 and copy line into the new array. Then you can assign the address of the new array to n[m].

The way it is now, line is assigned to cp but this only assigns the address of line[0]. Since line is a local variable the address of line[0] never changes and so cp never changes either. The array n elements are all the same address. The address of line[0].

Usually, malloc is used to allocate a new array of 1024 before each read. The address of the array would go into n[m]. Then you would read directly into n[m].