Hey everyone, in the following code, what should the result of d be after the second expression?
int d = 1;
d += d++;
One would assume d is 3 afterwards but the unary increment d++ doesn't seem to take effect and d retains a value of 2.
Is there a name for this bug? Does it exist for other compilers that support unary increment like C#?
If you take a look at the generated IL, you'll see why the result is 2 and not 3.
IL_0000: ldc.i4.1 // load constant 1 on evaluation stack
IL_0001: stloc.0 // pop and store value in local 0
IL_0002: ldloc.0 // load value of local 0 on evaluation stack
IL_0003: ldloc.0 // repeat, stack is now 1, 1
IL_0004: dup // duplicate topmost value on evaluation stack,
// i.e. stack is now 1, 1, 1
IL_0005: ldc.i4.1 // load constant 1 on evaluation stack
IL_0006: add // add two topmost values on stack,
// i.e. 1 and 1 and push result on stack
IL_0007: stloc.0 // pop and store this value in local 0
IL_0008: add // add the two remaining values on the stack
// which again happens to be 1 and 1 and push result to stack
IL_0009: stloc.0 // pop and store this value in local 0
In other words: The final value stored is the sum of 1 and 1.
(the code above is from release mode build)