https://ftp.gnu.org/old-gnu/Manuals/gdb/html_node/gdb_109.html

whatis expr

举例 whatis  uint64      ->   unsigned  long long

Print the data type of expression expr. expr is not actually evaluated, and any side-effecting operations (such as assignments or function calls) inside it do not take place. See section Expressions.whatisPrint the data type of $, the last value in the value history.ptype typenamePrint a description of data type typename. typename may be the name of a type, or for C code it may have the form `class class-name', `struct struct-tag', `unionunion-tag' or `enum enum-tag'.ptype exprptypePrint a description of the type of expression expr. ptype differs from whatis by printing a detailed description, instead of just the name of the type. For example, for this variable declaration:

struct complex {double real; double imag;} v;

the two commands give this output:

(gdb) whatis v

type = struct complex

(gdb) ptype v

type = struct complex {

    double real;

    double imag;

}