how extracts values from a char array?

Question

HI I have following char array in C,

char array[1024] = "My Message: 0x7ffff6be9600"

i have to extract the value "0x7ffff6be9600" only from above char array.

how can i extract the value with the use scanf() type functions?

Thanks in advance.

Do you want to extract it to a string or to an unsigned long long? — Matteo Italia
– Matteo Italia, Commented Sep 22, 2011 at 9:50

oh whatever · Accepted Answer · 2011-09-22 09:37:05Z

1

Use the sscanf function, precisely for that.

For example:

unsigned long l;
if (3 == sscanf(array, "%*s %*s %lx", &l)) //ignore the words before the number
{
    // got something
}

edited Sep 22, 2011 at 9:37

answered Sep 22, 2011 at 9:22

oh whatever

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2 Comments

pmg Over a year ago

your sscanf will "fail" when it sees the 1st character in "My Message"

nos Over a year ago

You'd first have to position array after the : , for this to work.

pmg · Accepted Answer · 2011-09-22 09:32:06Z

0

Look ma, no scanf ...

printf("%.14s", strstr(array, " 0x") + 1);

or, still no scanf

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

int main(void) {
  char array[] = "My Message: 0x7ffff6be9600----";
  char result[100];
  char *tmp;

  tmp = strstr(array, " 0x");
  if (tmp) {
    strncpy(result, strstr(array, " 0x") + 1, 14);
    result[14] = 0;
    printf("result: %s\n", result);
  } else {
    printf("invalid input\n");
  }
  return 0;
}

answered Sep 22, 2011 at 9:32

pmg

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Comments

Djole · Accepted Answer · 2011-09-22 10:23:07Z

Perhaps something like this would work for you :

char IsDigit(char val)
{
    if((val>47 && val<58))
        return 1;
    else if(val>64 && val<70)
        return 2;
    else if(val>96 && val<103)
        return 3;

    return 0;
}

__int64 GetHexInt64(char* text,int maxlen)
{
   int i=0;
   char state=0;
   char dig;
   __int64 res = 0;
   int digcnt = 0;

   while(i<maxlen && text[i]!='\0')
   {
      switch(state)
      {
         case 0:
         if(text[i]=='0')
             state++;
         else
             state=0;
         break;
        case 1:
           if(text[i]=='x' || text[i]=='X')
            state++;
           else
            state=0;
         break;
      }
      i++;

      if(state==2)
          break;
   }

   if(state!=2)
     return (__int64)-1;

   while(i<maxlen && text[i]!='\0' && digcnt<16)
   {
       dig = IsDigit(text[i]);
       if(dig)
       {
           digcnt++;
           switch(dig)
           {
           case 1:
               res<<=4;
               res|=(text[i]-48) & 0x0f;
               break;
           case 2:
               res<<=4;
               res|=(text[i]-55) & 0x0f;
               break;
           case 3:
               res<<=4;
               res|=(text[i]-87) & 0x0f;
               break;
           }
       }
       else
       {
           break;
       }

       i++;
   }
   return res;
}

Sorry about the __int64 but I am unsure what is the correct type for a 64-bit integer in your compiler.

johnsyweb · Accepted Answer · 2011-09-22 11:01:10Z

0

Here's a simple example using sscanf(), which is fairly close to scanf():

> cat 7512438.c
#include <stdio.h>

int main() {
    char array[1024] = "My Message: 0x7ffff6be9600";
    unsigned long hex = 0UL;
    if (sscanf(array, "My Message: 0x%lx", &hex) == 1) {
        printf("%lx\n", hex);
    } else {
        printf("Sorry, could not extract anything useful from %s\n", array);
    }
    return 0;
}

> make 7512438
cc  -Wall -I /opt/local/include -L/opt/local/lib  7512438.c   -o 7512438
> ./7512438    
7ffff6be9600

edited Sep 22, 2011 at 11:01

answered Sep 22, 2011 at 9:33

johnsyweb

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7 Comments

BSalunke Over a year ago

Thanks Johnsyweb, but im unable to extract it gives message "Sorry, could not extract anything useful from My Message: 0x7ffff6be9600 ".

johnsyweb Over a year ago

@BSalunke: Then your message must look different to the one you provided. I've updated my answer to demonstrate. Or see it here: ideone.com/tuqlh

BSalunke Over a year ago

Thanks,Johnsyweb its working fine, Im getting the value in a string i.e. hex. Now can u tell me how to convet that string to unsigned long so that i can call a function from that address.

johnsyweb Over a year ago

@BSalunke: I've updated the type of hex and the format strings accordingly.

BSalunke Over a year ago

ya, I am getting the address in unsigned long type variable but its missing 0x in that. can we get that also?

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