integral promotions

**St0rM-MaN** · 06-28-2007

hi all

Code:

#include<stdio.h>
#include<stdlib.h>

main()
{
        char x;
        char f;
        int z;

        x='f';
        f='d';
        z=x+f;

        printf("\n &#37;d , %d\n",x,f);
        printf("%d\n",z);

exit(EXIT_SUCCESS);

}

as my topic says i am asking about integral promotions
when integral promotion applied shouldn'y the value be an int in case it cane hold it and unsigned int in case int can not hold it
so
look at this code

Code:

#include<stdio.h>
#include<stdlib.h>

main()
{
        char x;
        char f;
        char z;

        x='f';
        f='d';
        z=x+f;

        printf("\n %d , %d\n",x,f);
        printf("%d\n",z);

exit(EXIT_SUCCESS);

}

it gives me the output -54 !!!!!!!! how this could be ?
shouldn'y it gives me error or somtehing that it cannot assgine value to this kind or variables ???
or i am getting the hall thing wrong ?
so my question is
how and where integral pormotions occures ?
thanks in advance

**St0rM-MaN** · 06-28-2007

if the new type can hold all of the values of the old type, then the value remains unchanged.

i did a samle search and i found this
that's mean it's occure in the expressions when it's required ?
and it's value assgined to the vraiable
if it can hold it the value is not changed but if it can't the precision is lost ?
thanks

**dwks** · 06-28-2007

Integral promotion occurs when you convert a smaller variable into a larger variable, for example a char into an int, or a long into a double.

As for why your last program outputs -54: you're adding 'f' and 'z' and storing the result in a char. This is 97 + 100, from an ASCII chart. This is 197, which is over 127, the maximum value that can be stored in a signed char (which is obviously what you implementation uses for "char"). So it wraps.

[edit] As for your second post, that sounds about right.

If the new type is larger (can hold more values) than the previous type, no data is lost. But if you cast downwards, from a large variable into a small variable, you might lose some data, depending on the actual value stored in the large variable. For example, (long)1 can be converted to a char properly, but (long)123456 cannot. [/edit]

**robwhit** · 06-28-2007

as a side note, char is supposed to be unsigned by default.

**dwks** · 06-28-2007

Nooo . . . it depends on the implementation. "char" can be "signed char" or "unsigned char", depending on the implementation. If you want a signed char or unsigned char, say so specifically.

[edit] And on nearly all platforms, "char" is the same as "signed char".

In fact, the keyword "signed" was added to the language so that you could use signed chars on platforms where the default char is unsigned. It's completely redundant in all other cases. [/edit]

**robwhit** · 06-28-2007

oh. thanks for setting me straight.

**St0rM-MaN** · 06-28-2007

thanks for both of you

**dwks** · 06-28-2007

Also, in case you're interested in the exact integer promotion rules, you can find them around. Here's one copy: http://www.devarticles.com/c/a/Cplus...ic-Data-Types/

I haven't read them, so I don't know how extensive they are. But if they are not in-depth enough for you, just use google to find some other page.

Thread: integral promotions

Thread Tools

Search Thread

Display

integral promotions

Similar Threads

How to convert integral types into pointer types?

Problem with Dawson's integral

integral counterpart to pow()?

Hashing non integral types

integral constant overflow error?