CODEWITHSUNDEEP
carrayspointersmalloc
bladepit
bladepit

Reputation: 873

Problems with dynamic array and pointer in C

I want to read the following lines from STDIN and save the values in c:

A:2
B:3
C:AAAA1
C:AASC2
C:aade3
D:1
D:199

Here is my c program:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <time.h>
#include <sys/time.h>

int main(int argc, char **argv)
{

    char buf[BUFSIZ];
    short a = 0;
    short b = 0;
    short anzb=0;
    short anza=0;
    char *c
    short *d;

    short i;


    while (fgets(buf, BUFSIZ, stdin) != NULL)
    {
        if (buf[strlen(buf)-1] == '\n') {
            char *isa = strstr(buf, "A:");
            char *isb = strstr(buf, "B:");
            char *isc = strstr(buf, "C:");
            char *isd = strstr(buf, "D:");
            if(isa){
                char *sep = substring(isa,3,strlen(isa));
                a = atoi(sep);
                d = malloc(a * sizeof(short));
            }else if(isb){
                char *sep = substring(isb,3,strlen(isb));
                b = atoi(sep);
                c = malloc(b * sizeof(char));
            }else if(isc){
                char *sep = substring(isc,3,strlen(isc));
                c[anzc] = sep;
                anzc++;
            }else if(isd){
                char *sep = substring(isd,3,strlen(isd));
                d[anzd] = sep;
                anzd++;
            }
        }
    }

    printf("%i\n", a);
    printf("%i\n", b);

    for(i=0; i<=anzc-1;i++){
        printf("%c", c[i]);
    }

    return 0;
}

I am new in c so i dont't have much knowledge about pointers and arrays so i hope you could help me.

After the values A: and B: are read and stored in a and b i could create my array for the lines of c and d. And i think here is my problem. I dont know how i could create an array at this time in my program. I tried with malloc and other things but there is my knowledge zu small for.

I only want to create an array at the time if i have read the values (sizes) for c and d (A and B).

And then i want to save the values in the array.

I hope you could help me to fix my code. I have tried much at this day but nothing worked and i am now very helpless.

EDIT:

New try where i get an segmentation fault 11:

     else if(isb){
        char *sep = substring(isb,8,strlen(isb));
        b = atoi(sep);
        c = malloc(b * sizeof(char*));
        int i;
        for (i = 0; i < subst; i++)
        {
          c[i] = malloc(13);
        }
    }else if(isc){
        char *sep = substring(isc,8,strlen(isc));
        strcpy(c[anzc], &buf[3]);
        anzc++;
    }

Upvotes: 1

Views: 242

Answers (1)

evanmcdonnal
evanmcdonnal

Reputation: 48076

Your allocation is more or less correct however you're overlooking some details. B provides you a value of 3, that is how many entries there are for C, not the length of each. You then allocated a single array when you in fact need a 2-D array which should be of type char* this array will point to 3 other arrays which will contain each of the values on the C lines. So;

This line c = malloc(b * sizeof(char)); needs to be c = malloc(b * sizeof(char*)); Then you need to do;

 int i;
 for (i = 0; i < b; i++)
 {
     c[i] = malloc(length); // where length is some arbitrary buffer length
     // because you have no way of knowing the length of the individual strings.
 }

After this you can use strcpy to copy the lines into each of the char arrays you've allocated in the for loop.

So to accomplish the copy you need to do something like this;

         int iC = 0;
         // outside of the while loop we need a control var track the index
         // of the c array. it needs to work independent of the normal iteration.
         //inside the while loop
         else if(isc){
            strcpy(c[iC], &buf[3]) 
            iC++;
        }

Upvotes: 1

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