declaration

I want to create an array with a message. $myArray = array('my message'); But using this code, myArray will get overwritten if it already existed. If I use array_push , it has to already exist. $myArray = array(); // <-- has to be declared first. array_push($myArray, 'my message'); Otherwise, it will bink. Is there a way to make the second example above work, without first clearing $myArray = array(); ? Check if the array exists first, and if it doesn't, create it...then add the element, knowing that the array will surely be defined before hand : if (!isset($myArray)) { $myArray = array(); }

Given # package main; our $f; sub f{} sub g {} 1; How can I determine that $f , but not $g , has been declared? Off the cuff, I'd thought that *{main::g}{SCALAR} might be undefined, but it is a bona fide SCALAR ref. Background: I'd like to import a variable into main:: , but carp or croak if that variable is already declared. EDIT Added an f subroutine in response to @DVK's initial answer. ANSWER (2010-07-27) This isn't easy, but it is possible. An eval technique is most portable, working on perls older than 5.10. In more recent perls, introspective modules like Devel::Peek and B can

The following code is allowed in C++: int a = a; or Type name = name; Both lead to an uninitialized object being initialized by itself, which often leads to undefined behavior. Is such code ever needed or reasonable? Are there cases of such code being useful? You are allowed to use the name of the variable in its initializer. The code Type name = name; is probably not useful, but the code Type name = f(&name); might be. There are many places where the language syntax doesn't forbid useless constructs. :-) adl This reminded me of an old thread of the GCC mailing list in which Gabriel Dos Reis

This fortran code was originally written in Fortran 77 format(I will show it later). After I got it, I changed it into f90 free format via a converting tool. Using intel fortran compiler ifort , the compiation and running is just as fine as before. Then I want to do more, I want to transform nonstandard，obsolete data type declaration f77 style like: real*8 , complex*16 etc into f90 standard real(8) , complex(16) . But I found an unbelievable thing. I just changed one "complex*16" into "complex(16)", then the running time increased from 10 seconds to 2 minutes. How could it be!!?? Can someone

Consider the following ways of declaring and initializing a variable of type C : C c1; C c2; c2 = C(); C c3(C()); C c4 = C(); Are all of these completely equivalent to each other, or can some of these differ depending on the exact definition of C ? (assuming it has public default and copy constructors). These mean: C c1; // default constructor C c2; // default constructor c2 = C(); // default constructor followed by assignment C c3(C()); // default constructor possibly followed by copy constructor C c4 = C(); // default constructor possibly followed by copy constructor Note the compiler can

I was reading a book when I found that array size must be given at time of declaration or allocated from heap using malloc at runtime.I wrote this program in C : #include<stdio.h> int main() { int n, i; scanf("%d", &n); int a[n]; for (i=0; i<n; i++) { scanf("%d", &a[i]); } for (i=0; i<n; i++) { printf("%d ", a[i]); } return 0; } This code works fine. My question is how this code can work correctly.Isn't it the violation of basic concept of C that array size must be declared before runtime or allocate it using malloc() at runtime.I'm not doing any of these two things,then why it it working