xcdoe4.2中，通过ARC来编译，总会遇到一些问题，比如原先使用c语言模块

很多时候，在使用Automatic Reference Counting的是时候，会提示一些很陌生的的错误提示，特别是使用conver to arc后，

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比如bridged cast?

给你的c代码上面加个_bridged。

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这里面有个详细的描述，

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A?bridged cast?is a C-style cast annotated with one of three keywords:

• (__bridge T) op?casts the operand to the destination type?T. If?T?is a retainable object pointer type, then?op?must have a non-retainable pointer type. If?T?is a non-retainable pointer type, then?op?must have a retainable object pointer type. Otherwise the cast is ill-formed. There is no transfer of ownership, and ARC inserts no retain operations.
• (__bridge_retained T) op?casts the operand, which must have retainable object pointer type, to the destination type, which must be a non-retainable pointer type. ARC retains the value, subject to the usual optimizations on local values, and the recipient is responsible for balancing that +1.
• (__bridge_transfer T) op?casts the operand, which must have non-retainable pointer type, to the destination type, which must be a retainable object pointer type. ARC will release the value at the end of the enclosing full-expression, subject to the usual optimizations on local values.

  These casts are required in order to transfer objects in and out of ARC control; see the rationale in the section on?conversion of retainable object pointers.

  Using a?__bridge_retained?or?__bridge_transfer?cast purely to convince ARC to emit an unbalanced retain or release, respectively, is poor form.

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  其实，你在apple llvm 的提示下面应该就能看到一些消息的描述，主要是说retain，这里面的bridge有unretained 和retained两种，说到这里面大家应该知道retain的含义了。

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  先写到这。

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  其实在这里面，跟多的是一些警告，让我决定很烦。

  比如隐式转换，和显示转换。