一、前言

　　LLDB是个开源的内置于XCode的具有REPL(read-eva l-print-loop)特征的Debugger，其可以安装C++或者Python插件。在日常的开发和调试过程中给开发人员带来了非常多的帮助。了解并熟练掌握LLDB的使用是非常有必要的。这篇文章将会带着大家一起了解在iOS开发中LLDB调试器的使用。

二、LLDB基础

2.1 LLDB基本语法

　　LLDB的基本语法如下

<command> [<subcommand> [<subcommand>...]] <action> [-options [option-value]] [argument [argument...]]

• <command>(命令)和<subcommand>(子命令)：LLDB调试命令的名称。命令和子命令按层级结构来排列：一个命令对象为跟随其的子命令对象创建一个上下文，子命令又为其子命令创建一个上下文，依此类推。

• <action>：执行命令的操作
• <options>：命令选项
• <arguement>：命令的参数
• []：表示命令是可选的，可以有也可以没有

　　举个例子，假设我们给main方法设置一个断点，我们使用下面的命令：

　　这个命令对应到上面的语法就是：

1. command: breakpoint 表示断点命令 
2. action: set 表示设置断点 
3. option: -n 表示根据方法name设置断点 
4. arguement: mian 表示方法名为mian　　

2.2 LLDB的基本使用

 2.2.1 Help命令　　

　　LLDB其中内置了非常多的功能，选择去硬背每一条指令并不是一个明智的选择。我们只需要记住一些常用的指令，在需要的时候通过help命令来查看相关的描述即可。

(lldb) help
Debugger commands:
  apropos           -- List debugger commands related to a word or subject.
  breakpoint        -- Commands for operating on breakpoints (see 'help b' for
                       shorthand.)
  bugreport         -- Commands for creating domain-specific bug reports.
  command           -- Commands for managing custom LLDB commands.
  disassemble       -- Disassemble specified instructions in the current
                       target.  Defaults to the current function for the
                       current thread and stack frame.
  expression        -- eva luate an expression on the current thread.  Displays
                       any returned value with LLDB's default formatting.
  frame             -- Commands for selecting and examing the current thread's
                       stack frames.
  gdb-remote        -- Connect to a process via remote GDB server.  If no host
                       is specifed, localhost is assumed.
  gui               -- Switch into the curses based GUI mode.
  help              -- Show a list of all debugger commands, or give details
                       about a specific command.
......

　　我们要查看某一个命令改如何使用时，可以使用 help <command> 来获取对应命令的使用方法。

(lldb) help expression
     eva luate an expression on the current thread.  Displays any returned value
     with LLDB's default formatting.  Expects 'raw' input (see 'help
     raw-input'.)

Syntax: expression <cmd-options> -- <expr>

Command Options Usage:
  expression [-AFLORTgp] [-f <format>] [-G <gdb-format>] [-a <boolean>] [-i <boolean>] [-t <unsigned-integer>] [-u <boolean>] [-l <source-language>] [-X <boolean>] [-v[<description-verbosity>]] [-j <boolean>] [-d <none>] [-S <boolean>] [-D <count>] [-P <count>] [-Y[<count>]] [-V <boolean>] [-Z <count>] -- <expr>
  expression [-AFLORTgp] [-a <boolean>] [-i <boolean>] [-t <unsigned-integer>] [-u <boolean>] [-l <source-language>] [-X <boolean>] [-j <boolean>] [-d <none>] [-S <boolean>] [-D <count>] [-P <count>] [-Y[<count>]] [-V <boolean>] [-Z <count>] -- <expr>
  expression [-r] -- <expr>
  expression <expr>

       -A ( --show-all-children )
            Ignore the upper bound on the number of children to show.

       -D <count> ( --depth <count> )
            Set the max recurse depth when dumping aggregate types (default is
            infinity).

。。。。。。

Examples:

    expr my_struct->a = my_array[3]
    expr -f bin -- (index * 8) + 5
    expr unsigned int $foo = 5
    expr char c[] = \"foo\"; c[0]
     
     Important Note: Bec