lua笔记之userdata

Posted 2020-08-06 mr_yu

1.一直使用框架里封装好的c库，想着自己一点一点的写些例子，学习下，以后需要c库，可以自己写了。

下边是一个简单的userdata的例子--数组操作。

newarray.c

#include "lua.h"
#include "lauxlib.h"
#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <string.h>

typedef struct NumArray
{
    int size;
    double values[1];
}NumArray;

static int 
lnew(lua_State *L)
{
    int arr_size = luaL_checkint(L, 1);
    if (arr_size <= 0)
    {
        assert(NULL);
    }

    size_t nbytes = sizeof(NumArray) + (arr_size - 1) * sizeof(double);
    NumArray *na = (NumArray *)lua_newuserdata(L, nbytes);
    na->size = arr_size;

    return 1;
}

static int 
lset(lua_State *L)
{
    NumArray *na = (NumArray *)lua_touserdata(L, 1);
    int idx = luaL_checkint(L, 2);
    double value = luaL_checknumber(L, 3);
    printf("idx %d, value %f\\n", idx, value);
    luaL_argcheck(L, na != NULL, 1, "array expected");
    luaL_argcheck(L, 1 <= idx && idx <= na->size , 2, "index out of range");

    na->values[idx - 1] = value;

    return 0;
}

static int 
lget(lua_State *L)
{
    NumArray *na = (NumArray *)lua_touserdata(L, 1);
    int idx = luaL_checkinteger(L, 2);

    luaL_argcheck(L, na != NULL, 1, "array expected");
    luaL_argcheck(L, 1 <= idx && idx <= na->size, 2, "index out of range");

    lua_pushnumber(L, na->values[idx - 1]);

    return 1;
}    
    
static int
lfind(lua_State *L)
{
    NumArray *na = (NumArray *)lua_touserdata(L, 1);
    assert(na != NULL);
    double elem = luaL_checknumber(L, 2);

    int idx;
    for (idx = 0; idx < na->size; idx++)
    {
        if (na->values[idx] == elem)
        {
            lua_pushnumber(L, idx + 1);
            return 1;
        }
    }

    lua_pushnumber(L, -1);
    return 1;
}

int
luaopen_newarray(lua_State *L)
{
    luaL_checkversion(L);
    luaL_Reg l[] = 
    {
        {"new", lnew},
        {"set", lset},
        {"get", lget},
        {"find", lfind},
        {NULL, NULL},
    };

    luaL_newlib(L, l);

    return 1;
}

编译这个c文件，生成动态库 , 命令: gcc -O2 -g -Wall -shared -fPIC -o newarray.so newarray.c -I/usr/include/lua5.2 -llua5.2当然我这里用的是lua5.2，用其它版本的需要更改-I,和-l的头文件和链接库的内容。

测试代码:test.lua

local newarray = require "newarray"

print(newarray)
local na = newarray.new(1000)

newarray.set(na, 1, 100)

local value = newarray.find(na, 100)

if value ~= -1 then
    print("value is ", value)
else
    print("not exists")
end

编译好newarray动态库，就可以运行测试代码了，安装lua是，编译后在src文件下有lua可执行文件，带着这个运行 ./.../lua test.lua.

结果如下:

先让程序跑起来，理解。

后续会加上详细讲解.望多多提意见，指正。。