为什么我必须在取消引用之前复制字符串? [英] Why must I copy string before dereferencing?

问题描述

要将值为字符串的映射转换为值为指向字符串的映射，我需要先复制字符串.如果我不这样做，则所有值都相同，可能是错误的值.为什么是这样?我不是在这里取字符串文字的地址.

To convert a map whose values are strings into one whose values are points to string, I need to copy the string first. If I do not, all the values are the same, potentially wrong value. Why is this? I am not taking the address of a string literal here.

func mapConvert (m map[string]string) map[string]*string {
    ret := make(map[string]*string)

    for k, v := range m {
        v2 := v[:]
        ret[k] = &v2
        // With the following instead of the last 2 lines, 
        // the returned map have the same, sometimes wrong value for all keys.
        // ret[k]=&v 
    }
    return ret
}

推荐答案

在函数 mapConvert 中有一个变量 v.应用程序将这个单一变量的地址用于映射中的每个键.

There is a single variable v in the function mapConvert. The application uses the address of this single variable for every key in the map.

通过为循环的每次迭代创建一个新变量来修复.使用映射中变量的地址.

Fix by creating a new variable for each iteration of the loop. Use the address of the variable in the map.

func mapConvert (m map[string]string) map[string]*string {
    ret := make(map[string]*string)

    for k, v := range m {
        v := v  // create a new 'v'.
        ret[k] = &v
    }
    return ret
}

请参阅 https://golang.org/doc/faq#closures_and_goroutines 了解说明并发上下文中的相同问题.

See https://golang.org/doc/faq#closures_and_goroutines for an explanation of the same problem in the context of concurrency.

这篇关于为什么我必须在取消引用之前复制字符串?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！