Query on type casting. 1

[isaisa]

Hi Everybody,
I Have one basic query on 'c' kind of type casting. i wanted to understand how type casting is handled at the compiler level. meaning what provisions are made and how the variable casted is treated by the compiler ???

thanks in advance...

sanjay

 

[ArkM]

handled at the compiler level? What is it?
Some examples:

/* Low-level i/o sample */
typedef struct Hdr { int x, y; } *Phdr;
char buff[100];
Phdr p;
...
if (fread(buff,1,100,f) >= sizeof(struct Hdr))
{
   p = (Phdr)buff; 
   /* as usually, do nothing (char* bits == p bits) 
    * char[] implicitly casted to char* then your cast...
    * Now the compiler knows that you know what to do...
    */
... 
/* Another case (may be you have specifications;) */
int n = 123;
...
printf("%f\n",(double)n); /* as usually, the compiler emits implicit RTL call */

May be it helps?
Or read books on theory of compilation...

 

[DaveSinkula]

i wanted to understand how type casting is handled at the compiler level. meaning what provisions are made and how the variable casted is treated by the compiler ?

A cast is an operator that performs a conversion. The compiler generates any code necessary to perform the conversion.

Preceding an expression by a parenthesized type name converts the value of the expression to the named type. This construction is called a cast.

Converting from floating point to integer is one example. The compiler might generate code the calls a function ("__ftol" perhaps) to perform the conversion.

Other conversions might be more trivial, such as converting an int to a char. The compiler might generate code that uses a "word" instruction or a "byte" instruction on the same memory location.

And yet other conversions, such as between pointers to differing data types, may appear to do nothing at all except get rid of a diagnostic message. This need not be the case since the representation of pointers to different types need not be the same.