* Vs ++ precedence in C

Question

I am not able to understand the output of the following C code :

#include<stdio.h>
main()
{
   char * something = "something";
   printf("%c", *something++);  // s
   printf("%c", *something);    // o
   printf("%c", *++something);  // m
   printf("%c", *something++);  // m
}

Please help :)

When writing code like this it is good to add some () to add readability since it much more clear what you like to happen with *(something++) or (*something)++. — Johan, Nov 12 '12 at 05:25
@Johan: yeah, I always have to look up if ++ or * is higher... and that after over 10 years of c++ ;-) I always do *(++something) — Mario The Spoon, Nov 12 '12 at 05:29
if any of the answers helped you, you shoul accept the answer ;-) — Mario The Spoon, Nov 12 '12 at 07:03

score 6 · Answer 1 · answered Nov 12 '12 at 05:24

See http://en.wikipedia.org/wiki/Operators_in_C_and_C%2B%2B#Operator_precedence for details

printf("%c", *something++);

Gets the char at *something and then increments it ('s')

printf("%c", *something);

Just get the char (now the second, due to the increment in the last statement ('o')

printf("%c", *++something);

increment and then get the char of the new position ( 'm' )

printf("%c", *something++);

Gets the char at *something and then increments it ('m')

score 6 · Answer 2 · edited May 23 '17 at 11:58

It is pretty simple.

char * something = "something";

Assignment of pointer.

printf("%c\n", *something++);//equivalent to *(something++)

Pointer is incremented but the value before increment is dereferenced ans it is post-increment.

printf("%c\n", *something);//equivalent to *(something)

Pointer is now pointing to 'o' after increment in the previous statement.

printf("%c\n", *++something);//equivalent to *(++something)

Pointer is incremented to point to 'm' and dereferenced after incrementing the pointer as this is pre-increment.

printf("%c\n", *something++);//equivalent to *(something++)

Same as the first answer. Also notice '\n' at the end of every string in printf. It makes the output buffer flush and makes the line print. Always use a \n at the end of your printf.

You may want to look at this question as well.

WhozCraig · Accepted Answer · 2012-12-20T12:05:41.437

// main entrypoint
int main(int argc, char *argv[])
{
    char * something = "something";

    // increment the value of something one type-width (char), then
    //  return the previous value it pointed to, to be used as the 
    //  input for printf.
    // result: print 's', something now points to 'o'.
    printf("%c", *something++);

    // print the characer at the address contained in pointer something
    // result: print 'o'
    printf("%c", *something);

    // increment the address value in pointer something by one type-width
    //  the type is char, so increase the address value by one byte. then
    //  print the character at the resulting address in pointer something.
    // result: something now points at 'm', print 'm'
    printf("%c", *++something);

    // increment the value of something one type-width (char), then
    //  return the previous value it pointed to, to be used as the 
    //  input for printf.
    // result: print 's', something now points to 'o'.
    printf("%c", *something++);
}

Result:

somm

@MarioTheSpoon *fantastic* name, sir. – WhozCraig Nov 12 '12 at 05:31 — WhozCraig, Nov 12 '12 at 05:31

score 0 · Answer 4 · edited Aug 09 '15 at 20:11

0

always use the clockwise rule clockwise rule

printf("%c\n", *something++);

according to the rule you will first encounter * so get the value then ++ means increment

enter image description here

in the 3rd case printf("%c\n", *something++);

enter image description here

so according to the image increment the value ++ and then get the value *

edited Aug 09 '15 at 20:11

Rakholiya Jenish

3,165
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answered Nov 12 '12 at 05:33

Bhavik Shah

5,125
3
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That's a good reference, but it's for types in declarations, not operators in expressions. – icktoofay Nov 12 '12 at 05:39
I tried it in this case and its working fine according to above solution I gave above. but you are right its for declarations. apologies if the answer is misleading – Bhavik Shah Nov 12 '12 at 05:42

* Vs ++ precedence in C

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