Inline functions vs Preprocessor macros


Preprocessor macros are just substitution patterns applied to your code. They can be used almost anywhere in your code because they are replaced with their expansions before any compilation starts.

Inline functions are actual functions whose body is directly injected into their call site. They can only be used where a function call is appropriate.

Now, as far as using macros vs. inline functions in a function-like context, be advised that:

  • Macros are not type safe, and can be expanded regardless of whether they are syntatically correct – the compile phase will report errors resulting from macro expansion problems.
  • Macros can be used in context where you don’t expect, resulting in problems
  • Macros are more flexible, in that they can expand other macros – whereas inline functions don’t necessarily do this.
  • Macros can result in side effects because of their expansion, since the input expressions are copied wherever they appear in the pattern.
  • Inline function are not always guaranteed to be inlined – some compilers only do this in release builds, or when they are specifically configured to do so. Also, in some cases inlining may not be possible.
  • Inline functions can provide scope for variables (particularly static ones), preprocessor macros can only do this in code blocks {…}, and static variables will not behave exactly the same way.


First, the preprocessor macros are just “copy paste” in the code before the compilation. So there is no type checking, and some side effects can appear

For example, if you want to compare 2 values:

#define max(a,b) ((a<b)?b:a)

The side effects appear if you use max(a++,b++) for example (a or b will be incremented twice). Instead, use (for example)

inline int max( int a, int b) { return ((a<b)?b:a); }

How do I UPDATE from a SELECT in SQL Server?


SET Table_A.col1 = Table_B.col1,
    Table_A.col2 = Table_B.col2
    Some_Table AS Table_A
    INNER JOIN Other_Table AS Table_B
        ON =
    Table_A.col3 = 'cool'

How to enable a non-global minor mode by default, on emacs startup?


I want to enable rainbow-mode everytime I start emacs, rather than having to use M-x rainbow-mode.

I guess there is some command I put in my .emacs file.

I tried all of the following, but none of them worked:

(require 'rainbow-mode)   

(rainbow-mode initialize)


More generally, how do I load any mode/package automatically on startup?


rainbow-mode isn’t a global minor mode, so it needs to be enabled on a per-buffer basis.

I only use it for CSS, so I have:

(add-hook 'css-mode-hook 'my-css-mode-hook)
(defun my-css-mode-hook ()
  (rainbow-mode 1))

If you genuinely want it to be global, everywhere, you can easily define a global minor mode yourself:

(define-globalized-minor-mode my-global-rainbow-mode rainbow-mode
  (lambda () (rainbow-mode 1)))

(my-global-rainbow-mode 1)

You can add any arbitrary logic to that (lambda () (rainbow-mode 1)) function (which will be evaluated in every buffer) in order to decide whether or not to actually call (rainbow-mode 1) for a given buffer, so if you’re comfortable with elisp then you can easily extend this approach to cover your specific requirements for the mode in question.

More generally, how do I load any mode/package automatically on startup?

It can vary, but the approaches I’ve shown would suffice for most minor modes: Either you want them enabled whenever MODE is enabled (being some specific other mode name), in which case you can use the MODE-hook variable (which will always be available) as per the css-mode-hookexample; or else you want the mode enabled permanently, in which case a global minor mode is a good approach (because you can toggle it on and off globally). Some minor modes are global by default (or provide global variants), but you can create your own if necessary, as per the my-global-rainbow-mode example.

Also be aware that modes can be derived from other modes, in which case all relevant MODE-hookhooks will be run (for details see A common use-case is to use prog-mode-hook to enable functionality wanted for all the programming modes which are derived from it (which is most programming modes).

Remember that many (hopefully most) libraries and packages will provide usage instructions. If you can’t find documentation, be sure to try M-x find-library to visit the library file, and then read through the comments at the top. There is often a very informative “Commentary” section, and sometimes this is the primary source of end-user documentation, and explain how to enable its functionality.


JavaScript – What’s the difference between using “let” and “var” to declare a variable?


The difference is scoping. var is scoped to the nearest function block and let is scoped to the nearest enclosing block, which can be smaller than a function block. Both are global if outside any block.

Also, variables declared with let are not accessible before they are declared in their enclosing block. As seen in the demo, this will throw a ReferenceError exception.



They are very similar when used like this outside a function block.

let me = 'go';  // globally scoped
var i = 'able'; // globally scoped

However, global variables defined with let will not be added as properties on the global windowobject like those defined with var.

console.log(; // undefined
console.log(window.i); // 'able'


They are identical when used like this in a function block.

function ingWithinEstablishedParameters() {
  let terOfRecommendation = 'awesome worker!'; //function block scoped
  var sityCheerleading = 'go!'; //function block scoped


Here is the difference. let is only visible in the for() loop and var is visible to the whole function.

function allyIlliterate() {
  //tuce is *not* visible out here

  for( let tuce = 0; tuce &lt; 5; tuce++ ) {
    //tuce is only visible in here (and in the for() parentheses)
    //and there is a separate tuce variable for each iteration of the loop

  //tuce is *not* visible out here

function byE40() {
  //nish *is* visible out here

  for( var nish = 0; nish &lt; 5; nish++ ) {
    //nish is visible to the whole function

  //nish *is* visible out here


Assuming strict mode, var will let you re-declare the same variable in the same scope. On the other hand, let will not:

'use strict';
let me = 'foo';
let me = 'bar'; // SyntaxError: Identifier 'me' has already been declared

'use strict';
var me = 'foo';
var me = 'bar'; // No problem, `me` is replaced.

chm viewer unable to show contents


I have a chm file that I can open at home. I use windows XP at home and at work. However, when I open the file at work it doesn’t show the contents of the file. It properly shows the TOC for the file though. Any ideas pls?


Other than what Nicolas suggested, you may not be able to see contents of a CHM that you open over a UNC path. If that is the case copy the file to a local drive.


Try to right-click on your chm file and select properties. You will see an “Unblock” button. Click on it, it should solve your problem.


just go to power shell and run it as administrator, cd your folder

and use the following command Unblock-File '.\filename.chm'


Unset key binding in emacs


The general way to unbind a key (for any keymap) is to define a binding of nil:

(define-key KEYMAP KEY nil)

For convenience, there are also two standard functions for unbinding from the global keymap and from the local keymap (which is usually the major mode’s keymap).

(global-unset-key KEY)
(local-unset-key KEY)

Those ones are interactive commands, as per their respective complements global-set-key and local-set-key.

As to your specific example, you probably want something like this:

(eval-after-load "zencoding-mode"
  '(define-key zencoding-mode-keymap (kbd "C-j") nil))

How to make occur mode select the window of buffer `*Occur*`?


Is it possible to make the occur mode grab the cursor (point)?, right now when I do M-x occur and search anything in a buffer, it will open the new buffer with the findings but the cursor stays in the buffer instead going to the findings.

I have to do C-x 0 to go to the other buffer everytime I do a search.

I tried doing it with a blank init.el just in case is helm or any other package, but I haven’t been able to make it focus the cursor on the new buffer.

( I know that there’s the helm-occur that does that, but is it possible with any command or function to make the cursor change to the active buffer when that command opens a new buffer? )

shareimprove this question

Occur has a hook, occur-hook, that contains a list of functions to run after a match is found. So we can add a hook to jump to the *Occur* window there:

(add-hook 'occur-hook
          '(lambda ()
             (switch-to-buffer-other-window "*Occur*")))