Lua obtains the field name in the table.

Suppose there is the following code:

 
 

  
  
local t = 
  
  
{
  
  
 a = 1,
  
  
 b = { x = 1, y = 2}
  
  
}
 
 

I will pass you a table and want to know which fields are in this table, but cannot be obtained directly. In this case, you can use the following method:

 
 

  
  
for k, v in pairs (t) do
  
  
 print(tostring(k), v)
  
  
end
 
 

We can see that it is okay to convert K into a field string using the tostring function.

However, we can also see that when a table is nested in a table, the nested table cannot be printed out. In this case, is there no way to do this?
Of course not. Someone has already implemented this common requirement. Here we will first provide the print_r version of Yunfeng.

 
 

  
  
Print a table in a tree shape,
  
  
@ Param: Root Node of the root table
  
  
function Utils.print_r(root)
  
  
 local cache = { [root] = "." }
  
  

  
  
 local function _dump(t,space,name)
  
  
 local temp = {}
  
  
 for k,v in pairs(t) do
  
  
 local key = tostring(k)
  
  
 if cache[v] then
  
  
 table.insert(temp,"+" .. key .. " {" .. cache[v].."}")
  
  
 elseif type(v) == "table" then
  
  
 local new_key = name .. "." .. key
  
  
 cache[v] = new_key
  
  
 table.insert(temp,"+" .. key .. _dump(v,space .. (next(t,k) and "|" or " " ).. string.rep(" ",#key),new_key))
  
  
 else
  
  
 table.insert(temp,"+" .. key .. " [" .. tostring(v).."]")
  
  
 end
  
  
 end
  
  
 return table.concat(temp,"\n"..space)
  
  
 end
  
  

  
  
 print(_dump(root, "" , ""))
  
  
end
 
 

As you can see, the X and Y fields in the nested table B have been printed, but this version is tree-like. If it is difficult to print complex table structures, at this time, you can take a look at the version

 
 

  
  
function Utils.print_lua_table (lua_table, indent)
  
  
 indent = indent or 0
  
  
 for k, v in pairs(lua_table) do
  
  
 if type(k) == "string" then
  
  
 k = string.format("%q", k)
  
  
 end
  
  
 local szSuffix = ""
  
  
 if type(v) == "table" then
  
  
 szSuffix = "{"
  
  
 end
  
  
 local szPrefix = string.rep(" ", indent)
  
  
 formatting = szPrefix.."["..k.."]".." = "..szSuffix
  
  
 if type(v) == "table" then
  
  
 print(formatting)
  
  
 print_lua_table(v, indent + 1)
  
  
 print(szPrefix.."},")
  
  
 else
  
  
 local szValue = ""
  
  
 if type(v) == "string" then
  
  
 szValue = string.format("%q", v)
  
  
 else
  
  
 szValue = tostring(v)
  
  
 end
  
  
 print(formatting..szValue..",")
  
  
 end
  
  
 end
  
  
end
 
 

Original: https://gist.github.com/rangercyh/5814003

However, this does not support key-value, so the function is quite tasteless. Please be careful when using it!

From Weizhi note (wiz)

Lua obtains the field name in the table.