expr is an expression (in the source language). By default the value of expr is printed in a format appropriate to its data type; you can choose a different format by specifying ‘/f’, where f is a letter specifying the format.
Another way of examining values of expressions and type information is through the Python extension command explore (available only if the gdb build is configured with –with-python). It offers an interactive way to start at the highest level (or, the most abstract level) of the data type of an expression (or, the data type itself) and explore all the way down to leaf scalar values/fields embedded in the higher level data types.
arg is either an expression (in the source language), or a type visible in the current context of the program being debugged.
In general, at any stage of exploration, you can go deeper towards the leaf values by responding to the prompts appropriately, or hit the return key to return to the enclosing data structure (the higher level data structure).
Similar to exploring values, you can use the explore command to explore types. Instead of specifying a value (which is typically a variable name or an expression valid in the current context of the program being debugged), you specify a type name. If you consider the same example as above, your can explore the type struct ComplexStruct by passing the argument struct ComplexStruct to the explore command.
By responding to the prompts appropriately in the subsequent interactive session, you can explore the type struct ComplexStruct in a manner similar to how the value cs was explored in the above example.
The explore command also has two sub-commands, explore value and explore type. The former sub-command is a way to explicitly specify that value exploration of the argument is being invoked, while the latter is a way to explicitly specify that type exploration of the argument is being invoked.
explore value expr
This sub-command of explore explores the value of the expression expr (if expr is an expression valid in the current context of the program being debugged). The behavior of this command is identical to that of the behavior of the explore command being passed the argument expr.
explore type arg
This sub-command of explore explores the type of arg (if arg is a type visible in the current context of program being debugged), or the type of the value/expression arg (if arg is an expression valid in the current context of the program being debugged). If arg is a type, then the behavior of this command is identical to that of the explore command being passed the argument arg. If arg is an expression, then the behavior of this command will be identical to that of the explore command being passed the type of arg as the argument.
You can use the command x (for “examine”) to examine memory in any of several formats, independently of your program’s data types.
Use the x command to examine memory.
n, f, and u are all optional parameters that specify how much memory to display and how to format it; addr is an expression giving the address where you want to start displaying memory. If you use defaults for nfu, you need not type the slash ‘/’. Several commands set convenient defaults for addr.
- n, the repeat count
The repeat count is a decimal integer; the default is 1. It specifies how much memory (counting by units u) to display. If a negative number is specified, memory is examined backward from addr.
- f, the display format
The display format is one of the formats used by print (‘x’, ‘d’, ‘u’, ‘o’, ‘t’, ‘a’, ‘c’, ‘f’, ‘s’), and in addition ‘i’ (for machine instructions). The default is ‘x’ (hexadecimal) initially. The default changes each time you use either x or print.
- u: the unit size The unit size is any of
- b Bytes.
- h Halfwords (two bytes).
- w Words (four bytes). This is the initial default.
- g Giant words (eight bytes).
The default for addr is usually just after the last address examined—but several other commands also set the default address: info breakpoints (to the address of the last breakpoint listed), info line (to the starting address of a line), and print (if you use it to display a value from memory).
- Support pretty-print(python): info pretty-printer
- info sharedlibrary: 显示关联的动态库
- info set 有环境变量？