CODEWITHSUNDEEP
c
Marco
Marco

Reputation: 368

warning: assignment makes integer from pointer without a cast with chars and strings

I keep getting segmentation faults on this code, I'm learning C at the moment.. Can anyone help me out?

Error location:

char *m;
char *as = concat("helloworld", buf);
*m = sha1(as);                               <<<<<< as
printf("%s\n", m);
free(as);

The concat function (not mine, used for joining 2 strings):

char* concat(char *s1, char *s2)
{
    size_t len1 = strlen(s1);
    size_t len2 = strlen(s2);
    char *result = malloc(len1+len2+1);//+1 for the zero-terminator
    //in real code you would check for errors in malloc here
    memcpy(result, s1, len1);
    memcpy(result+len1, s2, len2+1);//+1 to copy the null-terminator
    return result;
}

The sha1 function:

char *sha1( char *val ){

   int msg_length = strlen( val );
   int hash_length = gcry_md_get_algo_dlen( GCRY_MD_SHA1 );
   unsigned char hash[ hash_length ];
   char *out = (char *) malloc( sizeof(char) * ((hash_length*2)+1) );
   char *p = out;
   gcry_md_hash_buffer( GCRY_MD_SHA1, hash, val, msg_length );
   int i;
   for ( i = 0; i < hash_length; i++, p += 2 ) {
      snprintf ( p, 3, "%02x", hash[i] );
   }
   return out;
}

Since I'm asking, what do they mean with:

 //in real code you would check for errors in malloc here

Thanks in advance

Upvotes: 0

Views: 1004

Answers (4)

Marco
Marco

Reputation: 368

The problem was in *m:

char *m = sha1("helloworld");    < OK
*m = sha1("helloworld");         < fail

Upvotes: -2

Mihai Maruseac
Mihai Maruseac

Reputation: 21435

m = sha1(as);

*m dereferences the pointer, it means the character under the pointer.

As for malloc, if it cannot allocate memory if will return a NULL pointer. You should check for that.

Upvotes: 1

Dayal rai
Dayal rai

Reputation: 6606

change *m = sha1(as); to m = sha1(as);. *m is a char value not a char *.

Now second question:

in real code you would check for errors in malloc here

is all about error handling where you need to check returned pointer from malloc against NULL.

Upvotes: 1

Crowman
Crowman

Reputation: 25908

sha1() returns char *, so you need to change *m = sha1(as); to m = sha(as);. *m is of type char, not char *.

Upvotes: 1

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