通过lua自带例子学习lua 07 (3135)

-- Example 31 --[[

Standard Libraries

Lua has standard built-in libraries for common operations in
math, string, table, input/output & operating system facilities.

External Libraries

Numerous other libraries have been created: sockets, XML, profiling,
logging, unittests, GUI toolkits, web frameworks, and many more.

]]

-- Example 32 -- Standard Libraries - math.

-- Math functions:
-- math.abs, math.acos, math.asin, math.atan, math.atan2,
-- math.ceil, math.cos, math.cosh, math.deg, math.exp, math.floor,
-- math.fmod, math.frexp, math.huge, math.ldexp, math.log, math.log10,
-- math.max, math.min, math.modf, math.pi, math.pow, math.rad,
-- math.random, math.randomseed, math.sin, math.sinh, math.sqrt,
-- math.tan, math.tanh

print(math.sqrt(9), math.pi)


-------- Output ------

3 3.1415926535898

-- Example 33 -- Standard Libraries - string.

-- String functions:
-- string.byte, string.char, string.dump, string.find, string.format,
-- string.gfind, string.gsub, string.len, string.lower, string.match,
-- string.rep, string.reverse, string.sub, string.upper

print(string.upper("lower"),string.rep("a",5),string.find("abcde", "cd"))


-------- Output ------

LOWER aaaaa 3 4

-- Example 34 -- Standard Libraries - table.

-- Table functions:
-- table.concat, table.insert, table.maxn, table.remove, table.sort

a={2}
table.insert(a,3);
table.insert(a,4);
table.sort(a,function(v1,v2) return v1 > v2 end)
for i,v in ipairs(a) do print(i,v) end


-------- Output ------

1 4
2 3
3 2

-- Example 35 -- Standard Libraries - input/output.

-- IO functions:
-- io.close , io.flush, io.input, io.lines, io.open, io.output, io.popen,
-- io.read, io.stderr, io.stdin, io.stdout, io.tmpfile, io.type, io.write,
-- file:close, file:flush, file:lines ,file:read,
-- file:seek, file:setvbuf, file:write

print(io.open("file doesn't exist", "r"))


-------- Output ------

nil file doesn't exist: No such file or directory 2