指针数组 [英] array of pointers

问题描述

嗨


关于指针数组的问题。


以下是一个21元素的数组，每个都是一个指针

或者这是一个指向ONE数组的指针（听起来很奇怪）：


double * ydata [21];


假设这是21个指针我如何初始化

它们指向null？这是错的：


，i = 0; i = 20 i ++

ydata [i] = NULL;


并稍后在某处分配新的


for I = 0; i = 20 i ++

ydata [i] = new double [1000];

这曾经在C中工作，但不适用于C ++！

分配新的后我试试这个：

for（int i = 0; i< 1000; i ++）{

ydata [0] [i] = double （rev_data [i]）;

它只是崩溃。

为你的帮助提供


Kamran
< br>

解决方案

请参阅多维阵列上的faq部分

Raj

AFAIR

T * p [n]; //数组T *

T（* p）[n]; //指针T [n]

* Henrietta Denoue：

嗨

以下是一个21元素数组，每个都是一个指针
或者这是一个指向ONE数组的指针（听起来很奇怪）

double * ydata [21];


一个21元素的数组，每个元素都是一个指针。


假设这是21个指针我如何初始化
他们指向null？这是错的：

对于i = 0; i = 20 i ++
ydata [i] = NULL;


是的，这是错误的，无论是语法上（它不是C ++）还是意图。


最简单的方式是


double * ydata [21] = {};


并分配新的某处后来

对于i = 0; i = 20 i ++
ydata [i] = new double [1000];

这曾经在C中工作，但不适用于C ++！


从来没有用过C语言，它既不是C语言也不是C ++语法。


分配新语后我试试这个：

for（int i = 0; i< 1000; i ++）{
ydata [0] [i] = double（rev_data [i]）;

At只是崩溃了。

将该循环与之前的循环进行比较。


-

答：因为它弄乱了人们通常阅读文字的顺序。

问：为什么这么糟糕？

A：热门发布。

问：usenet和电子邮件中最烦人的事情是什么？

Hi

A question about array of pointers.

Is the following an 21 element array, each a pointer
or is this a pointer to ONE array (strange as it sounds):

double* ydata[21];

And supposing this to be 21 pointers how do I initialize
them to point to null ? Is this wrong:

for i=0; i=20 i++
ydata[i] = NULL;

and to allocate new somewhere later

for i=0; i=20 i++
ydata[i] = new double[1000];
This used to work in C but doesn''t with C++ !
After allocating new I try this:
for (int i = 0; i < 1000; i++) {
ydata[0][i] = double(rev_data[i]);
At it just crashes.
Thaks for your help

Kamran

解决方案

please see the faq section on multi-dimensional array
Raj

AFAIR
T *p[n]; //array of T*
T (*p)[n]; //pointer to T[n]

* Henrietta Denoue:

Hi

A question about array of pointers.

Is the following an 21 element array, each a pointer
or is this a pointer to ONE array (strange as it sounds)

double* ydata[21];
A 21 element array, each element a pointer.

And supposing this to be 21 pointers how do I initialize
them to point to null ? Is this wrong:

for i=0; i=20 i++
ydata[i] = NULL;

Yes, that is wrong, both syntactically (it''s not C++) and in intent.

Easiest way is

double* ydata[21] = {};

and to allocate new somewhere later

for i=0; i=20 i++
ydata[i] = new double[1000];
This used to work in C but doesn''t with C++ !
That has never worked in C, it''s neither C nor C++ syntax.

After allocating new I try this:
for (int i = 0; i < 1000; i++) {
ydata[0][i] = double(rev_data[i]);
At it just crashes.

Compare that loop to the previous ones.

--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?

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