C函数原型中怎么还可以有初始化？

查看了MSDN上的相关解释，好像确实有这个东西，但是在实际中好像有没有用到过，这是怎么回事？
declaration:
declaration-specifiers attribute-seq opt init-declarator-list opt;

/* attribute-seq opt is Microsoft Specific */

declaration-specifiers:
storage-class-specifier declaration-specifiers opt

type-specifier declaration-specifiers opt

type-qualifier declaration-specifiers opt

init-declarator-list:
init-declarator

init-declarator-list , init-declarator

init-declarator:
declarator

declarator = initializer

declarator:
pointer opt direct-declarator

direct-declarator: /* A function declarator */
direct-declarator ( parameter-type-list )      /* New-style declarator */

direct-declarator ( identifier-list opt )    /* Obsolete-style declarator */

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怎么没有人呀？

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耐着性子看完了剩下部分……

parameter-type-list:
      parameter-list
      parameter-list , ...
parameter-list:
      parameter-declaration
      parameter-list , parameter-declaration
parameter-declaration:
      declaration-specifiers declarator
      declaration-specifiers abstract-dec