Conversion of C + + middle number

Source: Internet
Author: User

Question: d=1,-d==?

Let's see what the answer will look like:


What is the output of the following code?

int main () {

Char dt = ' \1 ';

Long TDT;

TDT =-dt;

printf ("%ld\n", TDT);


My first reaction was that this output should be "-1". I think you think so, too. But what if the output is on a 64-bit system? I hope it is also "-1". Let's see if this is the case.

Let's test it.

#xlc-q64 a.c-qlanglvl=extended



!! The output here is "4294967295" instead of "1".

Don't worry, it's possible we missed something.

Before answering the previous question, let's look at the following code snippet:

"Char dt = ' \1 ';" -dt; "

For this code snippet, can we confirm that the DT variable is signed or unsigned? C

Let's look at what the C language standard says:

The implementation shall define char to have the same range, representation, and behavior as either signed char or Unsigne D Char.

This means that the standard does not require symbols for char type variables. We're looking at the XL compiler's documentation Http:// _ Ref/ch.html

Inside said:

By default, char behaves like a unsigned char. To change this default, can use The-qchars option or the #pragma chars directive. See-qchars for more information.

It appears that in the XL compiler, char defaults to unsigned. We can use-qchars to change this default behavior. Let's test this out:

#xlc-q64 a.c-qlanglvl=extended-qchar=signed



That's great. We seem to have understood.

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