Lua 学习 chapter28

topic
13k 词

目录

  1. 基础知识
  2. 操作表
  3. 一些简便方法
  4. 调用lua函数

回顾复习加巩固，自己应该认真地学习复习和巩固，并不是只有学习新知识是自己最重要的，而是复习和巩固才是自己最重要的，所以自己每天必须抽出一定的时间对自己的学习进行复习和巩固。

基础知识

lua可以作为配置文件来供c语言使用，例如我们来定义一个窗口的大小。

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width = 200
height = 300

然后我们使用LuaAPI来指挥lua语言解析该文件，并获取width和height的值。

  • luaL_loadfile(lua_State *L, fname):加载文件并且编译，返回一个执行这个文件的函数，放到栈顶
  • lua_pcall(L,0,0,0):调用栈中的函数，第二个参数为函数参数的个数，第三个参数为返回值的个数，第四个参数为错误处理函数。在压入结果之前，pcall函数会将参数和函数出栈，将返回值从第一个按照顺序压入栈中。至于最后一个参数为零，则lua会把错误信息作为string压倒栈中，如果是函数，第四个参数为它在栈中的索引，一般这个错误处理函数应该在被压入栈且位于待调用函数之下。
  • lua_getglobal(lua_State *L, const char *key):根据key值获取全局变量，并放到栈顶。
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#include<stdio.h>
#include<string.h>
#include<stdarg.h>
#include<stdlib.h>
extern "C" {
#include <lua.h>
#include <lauxlib.h>
#include <lualib.h>
}

int getglobint(lua_State L, const char var);

void load(lua_State L, const char fname, int w, int h);

void error(lua_State L, const char fmt, …);


int main(void)

{

lua_State* L = luaL_newstate();//打开lua

luaL_openlibs(L);//打开标准库


<span class="kt">int</span> <span class="n">width</span><span class="p">,</span> <span class="n">height</span><span class="p">;</span>
<span class="n">load</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="s">&#34;config&#34;</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">width</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">height</span><span class="p">);</span>
<span class="n">printf</span><span class="p">(</span><span class="s">&#34;%d %d&#34;</span><span class="p">,</span> <span class="n">width</span><span class="p">,</span> <span class="n">height</span><span class="p">);</span>
<span class="k">return</span> <span class="mi">0</span><span class="p">;</span>



}


int getglobint(lua_State L, const char var)

{

int isnum, result;

lua_getglobal(L, var);//将相应的全局变量的值压入到栈中。

result = (int)lua_tointegerx(L, -1, &isnum);

if (!isnum)

{

error(L, "'%s' should be a number n", var);

}

lua_pop(L, 1);

return result;

}


void load(lua_State L, const char fname, int w, int h)

{

if (luaL_loadfile(L,fname) || lua_pcall(L,0,0,0))//loadfile加载代码，pcall运行编译后的代码段

{

error(L, "cannot  run config. file %s", lua_tostring(L,-1));

}

w = getglobint(L, "width");

h = getglobint(L, "height");

}


void error(lua_State L, const char fmt, …)

{

va_list argp;

va_start(argp, fmt);

vfprintf(stderr, fmt, argp);

va_end(argp);

lua_close(L);

exit(EXIT_FAILURE);

}


}

操作表

现在我们要为每个窗口配置一种背景色，假设最终的颜色格式是由三个数字分量组成的RGB颜色。

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width = 200
height = 300
BLUE = {red = 0,green = 0,blue = 1.0}
background = BLUE

我们可以对表进行操作，具体用到的函数：

  • lua_pushstring(L,key)
  • lua_gettable(L,-2) //-2是表的索引，它会pop出key，然后根据key取值，并把值放到栈中
  • lua_getfield(L,-1,key)//相当于上面的两步，这个函数会返回结果的类型
  • lua_pushnumber(L,val)
  • lua_pushstring(L,key)
  • lua_settable(L,-3)// -3是表的索引，它会pop出val，key，然后给表设置值。
  • lua_setfield(L,-2,key)// 相当于上面的两步，它会pop出val然后根据key设置值。
  • lua_createtable(L,int narr,int nrec):narr,表示连续的值个数，nrec表示hash的值个数。
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#include<stdio.h>
#include<string.h>
#include<stdarg.h>
#include<stdlib.h>
extern "C" {
#include <lua.h>
#include <lauxlib.h>
#include <lualib.h>
}

const int MAX_COLOR = 255;


struct ColorTable

{

const char* name;

unsigned char red, green, blue;

}colortable[] = {

{"WHITE", MAX_COLOR, MAX_COLOR, MAX_COLOR},

{"RED", MAX_COLOR, 0, 0},

{"GREEN", 0, MAX_COLOR, 0},

{"BLUE", 0, 0, MAX_COLOR},

{NULL, 0, 0, 0}

};


int getglobint(lua_State L, const char var);

void load(lua_State L, const char fname, int w, int h);

void error(lua_State L, const char fmt, …);

void getColor(lua_State L, const char what, int r, int g, int b);

int getcolorfield(lua_State L, const char key);

void setcolor(lua_State L,struct ColorTable ct);

void setcolorfield(lua_State L, const char* index, int value);


int main(void)

{

lua_State* L = luaL_newstate();//打开lua

luaL_openlibs(L);//打开标准库


<span class="kt">int</span> <span class="n">width</span><span class="p">,</span> <span class="n">height</span><span class="p">,</span> <span class="n">red</span><span class="p">,</span> <span class="n">green</span><span class="p">,</span> <span class="n">blue</span><span class="p">;</span>
<span class="n">load</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="s">&#34;config&#34;</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">width</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">height</span><span class="p">);</span>
<span class="n">printf</span><span class="p">(</span><span class="s">&#34;%d %d </span><span class="se">n</span><span class="s">&#34;</span><span class="p">,</span> <span class="n">width</span><span class="p">,</span> <span class="n">height</span><span class="p">);</span>
<span class="n">getColor</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="s">&#34;background&#34;</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">red</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">green</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">blue</span><span class="p">);</span>
<span class="n">printf</span><span class="p">(</span><span class="s">&#34;%d</span><span class="se">t</span><span class="s">%d</span><span class="se">t</span><span class="s">%d</span><span class="se">n</span><span class="s">&#34;</span><span class="p">,</span> <span class="n">red</span><span class="p">,</span> <span class="n">green</span><span class="p">,</span> <span class="n">blue</span><span class="p">);</span>
<span class="kt">int</span> <span class="n">i</span> <span class="o">=</span> <span class="mi">0</span><span class="p">;</span>
<span class="k">while</span> <span class="p">(</span><span class="n">colortable</span><span class="p">[</span><span class="n">i</span><span class="p">].</span><span class="n">name</span> <span class="o">!=</span> <span class="nb">NULL</span><span class="p">)</span>
<span class="p">{</span>
	<span class="n">setcolor</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="o">&amp;</span><span class="n">colortable</span><span class="p">[</span><span class="n">i</span><span class="o">++</span><span class="p">]);</span>
<span class="p">}</span>
<span class="k">return</span> <span class="mi">0</span><span class="p">;</span>



}


int getglobint(lua_State L, const char var)

{

int isnum, result;

lua_getglobal(L, var);

result = (int)lua_tointegerx(L, -1, &isnum);

if (!isnum)

{

error(L, "'%s' should be a number n", var);

}

lua_pop(L, 1);

return result;

}


void load(lua_State L, const char fname, int w, int h)

{

if (luaL_loadfile(L,fname) || lua_pcall(L,0,0,0))

{

error(L, "cannot  run config. file %s", lua_tostring(L,-1));

}

w = getglobint(L, "width");

h = getglobint(L, "height");

}


void error(lua_State L, const char fmt, …)

{

va_list argp;

va_start(argp, fmt);

vfprintf(stderr, fmt, argp);

va_end(argp);

lua_close(L);

exit(EXIT_FAILURE);

}


void getColor(lua_State L, const char what, int r, int g, int* b)

{

lua_getglobal(L, what);

if (!lua_istable(L,-1))

{

error(L, "'%s' is not a table", what);

}


<span class="o">*</span><span class="n">r</span> <span class="o">=</span> <span class="n">getcolorfield</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="s">&#34;red&#34;</span><span class="p">);</span>
<span class="o">*</span><span class="n">g</span> <span class="o">=</span> <span class="n">getcolorfield</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="s">&#34;green&#34;</span><span class="p">);</span>
<span class="o">*</span><span class="n">b</span> <span class="o">=</span> <span class="n">getcolorfield</span><span class="p">(</span><span class="n">L</span><span class="p">,</span> <span class="s">&#34;blue&#34;</span><span class="p">);</span>



}


int getcolorfield(lua_State L, const char key)

{

int result, isnum;

lua_getfield(L, -1, key);

result = (int)(lua_tonumberx(L, -1, &isnum) * MAX_COLOR);

if (!isnum)

{

error(L, "invalid component '%s' in color", key);

}

lua_pop(L, 1);

return result;

}


void setcolor(lua_State L, ColorTable ct)

{

lua_newtable(L);

setcolorfield(L, "red", ct->red);

setcolorfield(L, "green", ct->green);

setcolorfield(L, "blue", ct->blue);

lua_setglobal(L, ct->name);

}


void setcolorfield(lua_State L, const char index, int value)

{

lua_pushstring(L, index);

lua_pushnumber(L, double(value) / MAX_COLOR);

lua_settable(L, -3);

//lua_setfield(L, -2, index); lua_setfield是将pushstring和settable结合起来的

}

调用lua函数

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//一个通用的调用函数
//这里vl其实就是一个指针，指向了参数的地址。
//
//va_start()所做的就是让vl指向函数的最后一个确定的参数（声明程序中是sig）的下一个参数的地址。
//
//va_arg()所做的就是根据vl指向的地址，和第二个参数所确定的类型，将这个参数的中的数据提取出来，作为返回值，同时让ap指向下一个参数。
//
//va_end()所做的就是让vl这个指针指向0。
void call_va(lua_State* L, const char* func, const char* sig, ...) {
	va_list vl;
	int narg, nres; //参数和结果的个数

<span class="n">va_start</span><span class="p">(</span><span class="n">vl</span><span c