Different answers from strlen and sizeof for Pointer & Array based init of String [duplicate]

Question

Possible Duplicates:
C: differences between pointer and array
Different sizeof results

Basically, I did this...

 char *str1 = "Sanjeev";
 char str2[] = "Sanjeev";
 printf("%d %d\n",strlen(str1),sizeof(str1));    
 printf("%d %d\n",strlen(str2),sizeof(str2));

and my output was

7 4
7 8

I'm not able to give reasons as to why the sizeof str1 is 4. Please explain the difference between these.

Answer 1

Because sizeof gives you the size in bytes of the data type. The data type of str1 is char* which 4 bytes. In contrast, strlen gives you the length of the string in chars not including the null terminator, thus 7. The sizeof str2 is char array of 8 bytes, which is the number of chars including the null terminator.

See this entry from the C-FAQ: http://c-faq.com/~scs/cclass/krnotes/sx9d.html

Try this:

 char str2[8];
 strncpy(str2, "Sanjeev", 7);
 char *str1 = str2;
 printf("%d %d\n",strlen(str1),sizeof(str1));    
 printf("%d %d\n",strlen(str2),sizeof(str2));

Answer 2

str1 is a pointer to char and size of a pointer variable on your system is 4.
str2 is a array of char on stack, which stores 8 characters, "s","a","n","j","e","e","v","\0" so its size is 8

Important to note that size of pointer to various data type will be same, because they are pointing to different data types but they occupy only size of pointer on that system.