得到命令的帮助信息

使用help命令可以得到gdb的命令帮助信息：

（1）help命令不加任何参数会得到命令的分类：

(gdb) help
List of classes of commands:

aliases -- Aliases of other commands
breakpoints -- Making program stop at certain points
data -- Examining data
files -- Specifying and examining files
internals -- Maintenance commands
obscure -- Obscure features
running -- Running the program
stack -- Examining the stack
status -- Status inquiries
support -- Support facilities
tracepoints -- Tracing of program execution without stopping the program
user-defined -- User-defined commands

Type "help" followed by a class name for a list of commands in that class.
Type "help all" for the list of all commands.
Type "help" followed by command name for full documentation.
Type "apropos word" to search for commands related to "word".
Command name abbreviations are allowed if unambiguous.

（2）当输入help class命令时，可以得到这个类别下所有命令的列表和命令功能：

(gdb) help data
Examining data.

List of commands:

append -- Append target code/data to a local file
append binary -- Append target code/data to a raw binary file
append binary memory -- Append contents of memory to a raw binary file
append binary value -- Append the value of an expression to a raw binary file
append memory -- Append contents of memory to a raw binary file
append value -- Append the value of an expression to a raw binary file
call -- Call a function in the program
disassemble -- Disassemble a specified section of memory
display -- Print value of expression EXP each time the program stops
dump -- Dump target code/data to a local file
dump binary -- Write target code/data to a raw binary file
dump binary memory -- Write contents of memory to a raw binary file
dump binary value -- Write the value of an expression to a raw binary file
......

（3）也可以用help command命令得到某一个具体命令的用法：

(gdb) help mem
Define attributes for memory region or reset memory region handling totarget-based.
Usage: mem auto
   mem <lo addr> <hi addr> [<mode> <width> <cache>],
where <mode>  may be rw (read/write), ro (read-only) or wo (write-only),
  <width> may be 8, 16, 32, or 64, and
  <cache> may be cache or nocache

（4）用apropos regexp命令查找所有符合regexp正则表达式的命令信息：

(gdb) apropos set
awatch -- Set a watchpoint for an expression
b -- Set breakpoint at specified line or function
br -- Set breakpoint at specified line or function
bre -- Set breakpoint at specified line or function
brea -- Set breakpoint at specified line or function
......

详情参见 gdb手册