doufei1988 2017-07-21 21:54
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为什么分配给指针会导致恐慌

I have the following code:

type box struct {
    val int
}

var p *box

This works fine:

p = &box{val: 2}

But this results in error:

*p = box{val: 2}

Error:

panic: runtime error: invalid memory address or nil pointer dereference 
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x5e59d9]

Why does the 2nd form of assignment result in panic?

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2条回答 默认 最新

  • donglian1953 2017-07-22 09:35
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    Because p points to nothing (nil). You must first allocate some memory and make p point to it before being allowed to deference p. You can use the new builtin to allocate memory initialised to the zero value of the pointed type.

    p = &box{val: 2}
    

    has the same result as:

    p = new(box)
    *p = box{val: 2}
    
    本回答被题主选为最佳回答 , 对您是否有帮助呢?
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