tonumber
Lua function

tonumber

Summary

Converts a string (of the given base) to a number

Prototype

n = tonumber (n, base)


Description

Converts n to a number using the optional base (default 10). Base can be from 2 to 36. For bases > 10 the letters a-z (not case sensitive) represent the digits. (eg. F is 15).
For decimal numbers you can supply fractions and exponents. Others should be unsigned.
Returns nil if the number cannot be converted.


print (tonumber ("100100", 2)) --> 36
print (tonumber ("1e5")) --> 100000
print (tonumber ("1EF", 16)) --> 495


You can use tonumber as a quick check if a variable contains something convertable to a number. 


print (tonumber ("abc")) --> nil
print (tonumber ("-43")) --> -43
print (tonumber (-43))   --> -43


To see if the variable actually is already a number type, use the "type" function:


print (type ("-43")) --> string
print (type (-43))   --> number


See also bit.tonumber which will handle larger numbers.

See Also ...

Topics

DOC_lua_base Lua base functions
DOC_lua_bc Lua bc (big number) functions
DOC_lua_bit Lua bit manipulation functions
DOC_lua_coroutines Lua coroutine functions
DOC_lua_debug Lua debug functions
DOC_lua_io Lua io functions
DOC_lua_math Lua math functions
DOC_lua_os Lua os functions
DOC_lua_package Lua package functions
DOC_lua_rex Lua PCRE regular expression functions
DOC_lua Lua script extensions
DOC_lua_string Lua string functions
DOC_lua_tables Lua table functions
DOC_lua_utils Lua utilities
DOC_scripting Scripting

Lua functions

LUA_assert assert (Asserts that condition is not nil and not false)
LUA_collectgarbage collectgarbage (Collects garbage)
LUA_dofile dofile (Executes a Lua file)
LUA_error error (Raises an error message)
LUA_gcinfo gcinfo (Returns amount of dynamic memory in use)
LUA_getfenv getfenv (Returns the current environment table)
LUA_getmetatable getmetatable (Returns the metatable for the object)
LUA_ipairs ipairs (Iterates over a numerically keyed table)
LUA_load load (Loads a chunk by calling a function repeatedly)
LUA_loadfile loadfile (Loads a Lua file and parses it)
LUA_loadlib loadlib (Loads a DLL (obsolete in Lua 5.1))
LUA_loadstring loadstring (Compiles a string of Lua code)
LUA_module module (Creates a Lua module)
LUA_next next (Returns next key / value pair in a table)
LUA_pairs pairs (Traverse all items in a table)
LUA_pcall pcall (Calls a function in protected mode)
LUA_print print (Prints its arguments)
LUA_rawequal rawequal (Compares two values for equality without invoking metamethods)
LUA_rawget rawget (Gets the value of a table item without invoking metamethods)
LUA_rawset rawset (Sets the value of a table item without invoking metamethods)
LUA_require require (Loads a module)
LUA_select select (Returns items in a list)
LUA_setfenv setfenv (Sets a function's environment)
LUA_setmetatable setmetatable (Sets the metatable for a table)
LUA_tostring tostring (Converts its argument to a string)
LUA_type type (Returns the type of a variable)
LUA_unpack unpack (Unpacks a table into individual items)
LUA_xpcall xpcall (Calls a function with a custom error handler)

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