This first edition was written for Lua 5.0. While still largely relevant for later versions, there are some differences.
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Re: Getting the key values from a table through the C API, Peter Odding; Re: Getting the key values from a table through the C API, RJP Computing; References:. Getting the key values from a table through the C API, RJP Computing; Prev by Date: Re: getting address of userdata Next by Date: Re: Getting the key values from a table through the C API.
.- Lua 5.0's string.gfind is still available, as well as 5.1's string.gmatch - C API Lua 5.0's luaLopenlib behavior is still available Changes:.
.Key Features The easiest way to learn Lua coding Use the Lua standard libraries and debug Lua code. CryENGINE Game Programming with C, C#, and Lua Get.
Lua (/ ˈ l uː ə / LOO-ə; from Portuguese: lua meaning moon) is a lightweight, high-level, multi-paradigm programming language designed primarily for embedded use in applications. Lua is cross-platform, since the interpreter of compiled bytecode is written in ANSI C, and Lua has a relatively simple C API to embed it into applications. Lua was originally designed in 1993 as a language for.

I need to create construction like this in Lua 5.1 C-API, not in Lua 5.2 and abovea =.

Programming in Lua

Part IV. The C APIChapter 25. Extending your Application

25.1 – Table Manipulation

Let us adopt that attitude:Now, we want to configure a background color for the window, too.We will assume that the final color specification is composedof three numbers,where each number is a color component in RGB.Usually, in C, those numbers are integers in some rangelike [0,255].In Lua, because all numbers are real,we can use the more natural range [0,1].

A naive approach here is to ask the user to set each componentin a different global variable:This approach has two drawbacks:It is too verbose(real programs may need dozens of different colors,for window background, window foreground, menu background, etc.);and there is no way to predefine common colors,so that, later,the user can simply write something like background = WHITE.To avoid these drawbacks, we will use a table to represent a color:The use of tables gives more structure to the script;now it is easy for the user (or for the application)to predefine colors for later use in the configuration file:To get these values in C, we can do as follows:As usual, we first get the value of the global variable backgroundand ensure that it is a table.Next, we use getfield to get each color component.This function is not part of the API;we must define it, as follows:Again, we face the problem of polymorphism:There are potentially many versions of getfield functions,varying the key type, value type, error handling, etc.The Lua API offers a single function, lua_gettable.It receives the position of the table in the stack,pops the key from the stack,and pushes the corresponding value.Our private getfield assumes that the table is on the top of the stack;so, after pushing the key (lua_pushstring),the table will be at index -2.Before returning, getfield pops the retrieved value from the stack,to leave the stack at the same level that it was before the call.

We will extend our example a little furtherand introduce color names for the user.The user can still use color tables,but she can also use predefined names for the more common colors.To implement this feature,we need a color table in our C application:

Our implementation will create global variables with the color namesand initialize these variables using color tables.The result is the same as if the user had the followinglines in her script:The only difference from these user-defined colors is thatthe application defines these colors in C,before running the user script.

To set the table fields,we define an auxiliary function, setfield;it pushes the index and the field value on the stack,and then calls lua_settable:Like other API functions,lua_settable works for many different types,so it gets all its operands from the stack.It receives the table index as an argumentand pops the key and the value.The setfield function assumes that before the callthe table is at the top of the stack (index -1);after pushing the index and the value,the table will be at index -3.

The setcolor function defines a single color.It must create a table, set the appropriate fields,and assign this table to the corresponding global variable:The lua_newtable function creates an empty tableand pushes it on the stack;the setfield calls set the table fields;finally, lua_setglobal pops the table andsets it as the value of the global with the given name.

With those previous functions,the following loop will register all colors inthe application's global environment:Remember that the application must execute this loopbefore running the user script.

There is another option for implementing named colors.Instead of global variables,the user can denote color names with strings,writing her settings as background = 'BLUE'.Therefore, background can be either a table or a string.With this implementation,the application does not need to do anything before runningthe user's script.Instead, it needs more work to get a color.When it gets the value of the variable background,it has to test whether the value has type string,and then look up the string in the color table:

What is the best option?In C programs,the use of strings to denote options is not a good practice,because the compiler cannot detect misspellings.In Lua, however, global variables do not need declarations,so Lua does not signal any error whena user misspells a color name.If the user writes WITE instead of WHITE,the background variable receives nil(the value of WITE, a variable not initialized),and that is all that the application knows:that background is nil.There is no other information about what is wrong.With strings, on the other hand,the value of background would be the misspelled string;so, the application can add that information to the error message.The application can also compare strings regardless of case,so that a user can write 'white', 'WHITE', or even 'White'.Moreover, if the user script is smalland there are many colors,it may be odd to register hundreds of colors(and to create hundreds of tables and global variables)only for the user to choose a few.With strings, you avoid this overhead.

Lua C Api Get Field Key Chain

Lua C Api Get Field Key

Programming in Lua

Part IV. The C APIChapter 28. User-Defined Types in C

28.3 – Object-Oriented Access

Our next step is to transform our new type into an object,so that we can operate on its instancesusing the usual object-oriented syntax,such as

Remember that a:size() is equivalent to a.size(a).Therefore, we have to arrange for the expression a.size to return ourgetsize function.The key mechanism here is the __index metamethod.For tables, this metamethod is called whenever Lua cannot finda value for a given key.For userdata, it is called in every access,because userdata have no keys at all.

Lua C Api Get Field Key West

Assume tha