Compiling expressions

Compiling expressions

[Antonio Eduardo Fermiano]

This is the third newbie question I make here, but...

If I put, for example:

variable = 1 + 2;

gcc will compile the code for the CPU add one to two and put in
variable, in execution time, or will substitute and in the compiled
code the equivalent of:

variable  = 3;

would be inserted?

If it evaluate expressions like this before compiling, it always is
done? Or I would need some directive to ask gcc to evaluate it for me
before compiling?

Thank you :)

Re: Compiling expressions

[Andrew Haley]

Antonio Eduardo Fermiano writes:
 > This is the third newbie question I make here, but...
 > 
 > If I put, for example:
 > 
 > variable = 1 + 2;
 > 
 > gcc will compile the code for the CPU add one to two and put in
 > variable, in execution time, or will substitute and in the compiled
 > code the equivalent of:
 > 
 > variable  = 3;
 > 
 > would be inserted?
 > 
 > If it evaluate expressions like this before compiling, it always is
 > done? Or I would need some directive to ask gcc to evaluate it for me
 > before compiling?

gcc always at compile time substitutes 3 for the expression 1 + 2 .

Andrew.

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Re: Compiling expressions

[龙海涛]

On Sat, 2007-12-15 at 15:11 -0200, Antonio Eduardo Fermiano wrote:
> This is the third newbie question I make here, but...
> 
> If I put, for example:
> 
> variable = 1 + 2;
> 
> gcc will compile the code for the CPU add one to two and put in
> variable, in execution time, or will substitute and in the compiled
> code the equivalent of:
> 
> variable  = 3;
> 
> would be inserted?
> 
> If it evaluate expressions like this before compiling, it always is
> done? Or I would need some directive to ask gcc to evaluate it for me
> before compiling?

i think you can search "constant folding" for more information

> 
> Thank you :)