Sponsored Content
Full Discussion: Extern variable.
Top Forums Programming Extern variable. Post 302219549 by spirtle on Tuesday 29th of July 2008 12:17:46 PM
Old 07-29-2008
So, the gcc linker appears not to insist on the extern qualifier.
It looks in fact like the compler and linker is happy that a1 is declared and tacitly assumes the extern and the definition -- recall the difference in C between definition of a variable, which tells the compiler to allocate memory for it, and the declaration, which tells the compiler what type it is. The distinction is apparent in global variables, where
Code:
int foo = 3;

is both definition and declaration, but
Code:
extern int foo;

is just a declaration -- it says that a1 is of type int but memory for it is allocated elsewhere.

Note that
  1. If you define a1 in bothe file1.c and file2.c, e.g.
    Code:
    int a1 = 2;

    then the linker does complain
  2. If you compile bothe files in the same compilation unit, e.g.
    Code:
    gcc -o file12.o -c file1.c file2.c

    then the compiler complains.

The a1 variable in file2.c is protected by the lexical scope of the function next and so is completely different to the global int a1.
 

10 More Discussions You Might Find Interesting

1. Programming

extern for functions

Hi, Please let me know if the extern keyword is necessary for using functions which is defined and declared in another file and and used in a different file where both these files are linked together. thanks (8 Replies)
Discussion started by: naan
8 Replies

2. Linux

Problem mounting extern hd (fedora 9)

Hi there, I'm having a bit of a strange problem which I would appreciate some help with. The Problem: I have two external hard drives, but I'm borrowing one off my parents to copy data too (one of mine, which is identical to theirs - WD MyBook 300g - is on its way out). Fedora 9 recognizes... (3 Replies)
Discussion started by: lasthidingplace
3 Replies

3. UNIX for Dummies Questions & Answers

fetchmail and forward to an extern address

Hi, I'm searching for an solution for the following problem. I want fetch some mails via pop3 from a@a.com with fetchmail. That works perfectly. Now any incoming mail should forwarded to b@b.com via smtp obv. But I don't know how to configure that. All online tutorials describe forwarding to... (0 Replies)
Discussion started by: mcW
0 Replies

4. Shell Programming and Scripting

Insert a line including Variable & Carriage Return / sed command as Variable

I want to instert Category:XXXXX into the 2. line something like this should work, but I have somewhere the wrong sytanx. something with the linebreak goes wrong: sed "2i\\${n}Category:$cat\n" Sample: Titel Blahh Blahh abllk sdhsd sjdhf Blahh Blah Blahh Blahh Should look like... (2 Replies)
Discussion started by: lowmaster
2 Replies

5. Shell Programming and Scripting

How to define a variable with variable definition is stored in a variable?

Hi all, I have a variable say var1 (output from somewhere, which I can't change)which store something like this: echo $var1 name=fred age=25 address="123 abc" password=pass1234 how can I make the variable $name, $age, $address and $password contain the info? I mean do this in a... (1 Reply)
Discussion started by: freddy1228
1 Replies

6. Programming

segmentation fault for extern

Why this is happening when both of them compiled together and run? I am getting segmentation fault SIGSEGV. File1.c: int arr; File2.c: extern int *arr; int main() { arr = 100; } (3 Replies)
Discussion started by: royalibrahim
3 Replies

7. Red Hat

How to pass value of pwd as variable in SED to replace variable in a script file

Hi all, Hereby wish to have your advise for below: Main concept is I intend to get current directory of my script file. This script file will be copied to /etc/init.d. A string in this copy will be replaced with current directory value. Below is original script file: ... (6 Replies)
Discussion started by: cielle
6 Replies

8. Shell Programming and Scripting

[Solved] How to increment and add variable length numbers to a variable in a loop?

Hi All, I have a file which has hundred of records with fixed number of fields. In each record there is set of 8 characters which represent the duration of that activity. I want to sum up the duration present in all the records for a report. The problem is the duration changes per record so I... (5 Replies)
Discussion started by: danish0909
5 Replies

9. Programming

C header file and extern

In the header file data.h i got: const char ack_msg = "ack: received your msg\n"; In the code file server.c i got: extern const char ack_msg; And else it is only used in a function call: user$ grep ack_msg *c *h server.c:extern const char ack_msg; server.c: n = write(clientsfd,... (5 Replies)
Discussion started by: tornow
5 Replies

10. Programming

Extern keyward on function in C

I saw a header (.h) file with mixture of "regular" function declarations and other extern function declarations. As I was told all function declarations are implicitly external and the extern on functions declarations is superfluous. Here my focus is on function declaration, not variable yet. int... (2 Replies)
Discussion started by: yifangt
2 Replies
Graphics::Primitive::Component(3pm)			User Contributed Perl Documentation		       Graphics::Primitive::Component(3pm)

NAME
Graphics::Primitive::Component - Base graphical unit DESCRIPTION
A Component is an entity with a graphical representation. SYNOPSIS
my $c = Graphics::Primitive::Component->new({ origin => Geometry::Primitive::Point->new({ x => $x, y => $y }), width => 500, height => 350 }); LIFECYCLE
prepare Most components do the majority of their setup in the prepare. The goal of prepare is to establish it's minimum height and width so that it can be properly positioned by a layout manager. $driver->prepare($comp); layout This is not a method of Component, but a phase introduced by the use of Layout::Manager. If the component is a container then each of it's child components (even the containers) will be positioned according to the minimum height and width determined during prepare. Different layout manager implementations have different rules, so consult the documentation for each for details. After this phase has completed the origin, height and width should be set for all components. $lm->do_layout($comp); finalize This final phase provides and opportunity for the component to do any final changes to it's internals before being passed to a driver for drawing. An example might be a component that draws a fleuron at it's extremities. Since the final height and width isn't known until this phase, it was impossible for it to position these internal components until now. It may even defer creation of this components until now. It is not ok to defer all action to the finalize phase. If you do not establish a minimum hieght and width during prepare then the layout manager may not provide you with enough space to draw. $driver->finalize($comp); draw Handled by Graphics::Primitive::Driver. $driver->draw($comp); METHODS
Constructor new Creates a new Component. Instance Methods background_color Set this component's background color. border Set this component's border, which should be an instance of Border. callback Optional callback that is fired at the beginning of the "finalize" phase. This allows you to add some sort of custom code that can modify the component just before it is rendered. The only argument is the component itself. Note that changing the position or the dimensions of the component will not re-layout the scene. You may have weird results of you manipulate the component's dimensions here. class Set/Get this component's class, which is an abitrary string. Graphics::Primitive has no internal use for this attribute but provides it for outside use. color Set this component's foreground color. fire_callback Method to execute this component's "callback". get_tree Get a tree for this component. Since components are -- by definiton -- leaf nodes, this tree will only have the one member at it's root. has_callback Predicate that tells if this component has a "callback". height Set this component's height. inside_bounding_box Returns a Rectangle that defines the edges of the 'inside' box for this component. This box is relative to the origin of the component. inside_height Get the height available in this container after taking away space for padding, margin and borders. inside_width Get the width available in this container after taking away space for padding, margin and borders. margins Set this component's margins, which should be an instance of Insets. Margins are the space outside the component's bounding box, as in CSS. The margins should be outside the border. maximum_height Set/Get this component's maximum height. Used to inform a layout manager. maximum_width Set/Get this component's maximum width. Used to inform a layout manager. minimum_height Set/Get this component's minimum height. Used to inform a layout manager. minimum_inside_height Get the minimum height available in this container after taking away space for padding, margin and borders. minimum_inside_width Get the minimum width available in this container after taking away space for padding, margin and borders. minimum_width Set/Get this component's minimum width. Used to inform a layout manager. name Set this component's name. This is not required, but may inform consumers of a component. Pay attention to that library's documentation. origin Set/Get the origin point for this component. outside_height Get the height consumed by padding, margin and borders. outside_width Get the width consumed by padding, margin and borders. finalize Method provided to give component one last opportunity to put it's contents into the provided space. Called after prepare. padding Set this component's padding, which should be an instance of Insets. Padding is the space inside the component's bounding box, as in CSS. This padding should be between the border and the component's content. page If true then this component represents stand-alone page. This informs the driver that this component (and any children) are to be renderered on a single surface. This only really makes sense in formats that have pages such as PDF of PostScript. prepare Method to prepare this component for drawing. This is an empty sub and is meant to be overridden by a specific implementation. preferred_height Set/Get this component's preferred height. Used to inform a layout manager. preferred_width Set/Get this component's preferred width. Used to inform a layout manager. to_string Get a string representation of this component in the form of: $name $x,$y ($widthx$height) visible Set/Get this component's visible flag. width Set/Get this component's width. AUTHOR
Cory Watson, "<gphat@cpan.org>" BUGS
Please report any bugs or feature requests to "bug-geometry-primitive at rt.cpan.org", or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Geometry-Primitive <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Geometry-Primitive>. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes. COPYRIGHT &; LICENSE Copyright 2008-2009 by Cory G Watson. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. perl v5.12.3 2011-06-02 Graphics::Primitive::Component(3pm)
All times are GMT -4. The time now is 06:07 AM.
Unix & Linux Forums Content Copyright 1993-2022. All Rights Reserved.
Privacy Policy