划横线的在这有什么用 啊。。

[冲tm的]

如图求助。。

[幻夢之葉]

定义别名：即MyPtr 是类型 tag* 的别名

[赵4老师]

typedef typedef type-declaration synonym; The typedef keyword defines a synonym for the specified type-declaration. The identifier in the type-declaration becomes another name for the type, instead of naming an instance of the type. You cannot use the typedef specifier inside a function definition. A typedef declaration introduces a name that, within its scope, becomes a synonym for the type given by the decl-specifiers portion of the declaration. In contrast to the class, struct, union, and enum declarations, typedef declarations do not introduce new types — they introduce new names for existing types. Example // Example of the typedef keyword typedef unsigned long ulong; ulong ul; // Equivalent to "unsigned long ul;" typedef struct mystructtag { int i; float f; char c; } mystruct; mystruct ms; // Equivalent to "struct mystructtag ms;" typedef int (*funcptr)(); // funcptr is synonym for "pointer // to function returning int" funcptr table[10]; // Equivalent to "int (*table[10])();"

[自信男孩]

typedef是定义别名。即MyType是struct tag的别名，而MyPtr是struct tag *的别名。