与输入字符指针与字符数组 [英] Input with char pointer vs. char array

问题描述

考虑code

#include<stdio.h>
int main(void)
{
   char* a;
   scanf("%s",a);//&a and &a[0] give same results-crashes 
   printf("%s",a);
   return 0;
}

为什么在这个崩溃code的结果？而使用字符数组这个code正常工作？

why does this code results in crashing?whereas this code using character array works fine?

#include<stdio.h>
int main(void)
{
   char a[100];
   scanf("%s",&a[0]);//works fine
   printf("%s",a);
   return 0;
}

区别在于字符数组和指针，但我知道，指针正好指向是与放大器的第一个元素; A [0]应该工作正常，但上code崩溃所有三个那就是，和放大器;一个和＆放大器;一个[0]？
最主要的，我会收集是我如何可以采取一个字符指针的输入，如果我坚持只能用scanf函数？
我道歉，如果我不明白。
在此先感谢:)

the difference being character array and pointer?but i knew that pointer just points to the first element that is &a[0] should work fine but upper code crashes for all three that is a,&a and &a[0]? the main thing i would to gather is how can i take input of a character pointer if i insist on using scanf only? i apologize if i am not clear. thanks in advance:)

推荐答案

由于的char * A; 分配堆栈的字符指针，而烧焦[100]; 为100个字符分配空间

Because char* a; allocates space on the stack for a character pointer whilst char a[100]; allocates space for 100 characters.

在前者的情况下，你需要分配一定的实际的内存的指针指向。发生了什么事使你崩溃的是， A 被设置为某个任意值（你不初始化它），当你 scanf函数，这是该数据被写入的位置。那如果你只是使用 A ，让我们叫那一声类型号之一。

In the former case, you need to allocate some actual memory for the pointer to point to. What's happening to cause your crash is that a is being set to some arbitrary value (you don't initialise it) and, when you scanf, that's where the data is being written. That's if you just use a, let's call that crash type number one.

如果您使用＆放大器;一个，它会写在指针本身，这将让你与点谁也不知道的，其中一个指针您的输入，从而导致崩溃输入两个数字。这是假设你没有输入的字符数大于将溢出的指针 - 这会破坏调用堆栈导致没有的其他的死机的情况（三类）

If you use &a, it will write your input over the pointer itself which will leave you with a pointer that points who-knows-where, leading to crash type number two. That's assuming you haven't entered more characters than will overflow the pointer - that would corrupt the call stack leading to yet another crash situation (type three).

和作为一句忠告，请不要使用没有边界检查，除非你控制是绝对以什么数据psented他们$ P $输入功能。即使有一个的char [100] ，有人可能会比将适合您的缓冲区中输入更多的字符会导致你的code堆栈溢出。

And as a word of advice, please don't use input functions that don't have bounds checking unless you're absolutely in control as to what data is presented to them. Even with a char[100], someone could cause a stack overflow in your code by entering more characters than will fit in your buffer.

我觉得做的最好的事情就是用与fgets （其中可以的限制字符读）连同 sscanf的（虽然如果所有你得到是一个字符串，的sscanf 是不是真的需要）。

I find the best thing to do is to use fgets (which can limit the characters read) in conjunction with sscanf (although if all you're getting is a string, sscanf is not really needed).

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