Undefined Value - Revision history

Arjun Suresh: /* Precedence Rule Violated? No */

2014-08-23T08:53:38Z

‎Precedence Rule Violated? No

2014-08-20T15:47:57Z

2014-08-20T15:46:12Z

2014-08-19T11:35:15Z

‎{{Template:Author|Arjun Suresh|{{arjunweb}} }}

2014-08-19T11:33:59Z

‎Other Examples for Undefined behaviour

2014-08-19T11:28:50Z

‎Other Examples for Undefined behaviour

2014-08-19T11:28:34Z

‎Other Examples for Undefined behaviour

2014-08-19T11:27:45Z

‎Other Examples for Undefined behaviour

2014-08-19T08:18:19Z

2014-08-19T08:17:28Z

@@ Line 97: / Line 97: @@
 After applying precedence rule, we get
   y = ((x++) * (++x));
 $x$++ or ++$x$ can happen first. Suppose ++$x$ happened first. It'll surely return $x+1$. But whether this incremented $x$ is used by $x$++ is not guaranteed. This increment can happen to $x$ ANYTIME before the next sequence point, which here is the ; at the end of the expression. This makes this code produce undefined behaviour.
 ==Other Examples for Undefined behaviour==

@@ Line 83: / Line 83: @@
-===Precedence Rule Violated? No===
+==Precedence Rule Violated? No==
 Undefined behaviour is happening not because C is violating precedence rule. Precedence (and associativity which is used when precedence of operators are same) rule is used to specify the operands for operations. But the actual execution order might be different. For example:
   x = a*b+c*d;
@@ Line 93: / Line 93: @@
 Similarly, if we take
-  x = i++ * ++i;
+  y = x++ * ++x;
 After applying precedence rule, we get
-  x = ((i++) * (++i));
+  y = ((x++) * (++x));
-$i$++ or ++$i$ can happen first. Suppose ++$i$ happened first. It'll surely return $i+1$. But whether this incremented $i$ is used by $i$++ is not guaranteed. This increment can happen to $i$ ANYTIME before the next sequence point, which here is the ; at the end of the expression. This makes this code produce undefined behaviour.
+$x$++ or ++$x$ can happen first. Suppose ++$x$ happened first. It'll surely return $x+1$. But whether this incremented $x$ is used by $x$++ is not guaranteed. This increment can happen to $x$ ANYTIME before the next sequence point, which here is the ; at the end of the expression. This makes this code produce undefined behaviour.

@@ Line 81: / Line 81: @@
   asuresh@parambara:~$ ./a.out
 1 2
 ==Other Examples for Undefined behaviour==

@@ Line 37: / Line 37: @@
 is undefined. In a function call in C, the order in which the argument expressions are processed is not defined. The only thing defined is that all arguments must be processed before the next sequence point- which here is the start of execution of the called function.
-Undefined value means compiler can give any value. i.e.; different compilers or even different versions of the same compiler can give different answers. As per C standard, no programmer should write this code. This is different from compiler dependent, in which case the output is clearly defined by the compiler and programmer can write those code as long as he is aware of the compiler. Example of compiler dependent code is sizeof(int).
+Undefined value means compiler can give any value. i.e.; different compilers or even different versions of the same compiler can give different answers. As per C standard, no programmer should write this code. This is different from compiler defined, in which case the output is clearly defined by the compiler and programmer can write those code as long as he is aware of the compiler. Example of compiler defined code is sizeof(int).
 ==Still undefined==

@@ Line 86: / Line 86: @@
   i = i++;
   printf("%d\n", i);
-  Possible outputs: 3, 2
+  Possible outputs: {3, 2}
   int i = 2;
@@ Line 95: / Line 95: @@
   j = (i++) * (++i);
   printf("%d", j);
-  Possible outputs: 6, 9
+  Possible outputs: {6, 9}
   int i = 2;
   printf("%d %d", i, i++);
-  Possible outputs: (2,3), (2,2)
+  Possible outputs: {(2,3), (2,2)}
 {{Template:FBD}}

@@ Line 82: / Line 82: @@
 1 2
-==Other Examples==
+==Other Examples for Undefined behaviour==
   i = i++;
   a[i] = i++;