指向字符串变量的指针的问题 [英] Question on pointer to string variable

问题描述

Hello Guys，



我有一个关于c launguage编程的问题。 （也适用于c ++）



问题：在主要的，我有一个指向字符串变量的指针，让我们说char * p。我从main调用函数func1（）。我想做以下。

1）在func1（）内部，我想使用malloc方法为p分配20个字节，后来我想将Hello word复制到字符串变量中。

2）函数调用（func1（））之后，我想打印p变量中的值。



我该怎么做？





问候，

Joy

Hello Guys,

I have one question on programming in c launguage. ( valid for c++ as well)

Question: In the main, I have a pointer to string variable, lets say char *p . I am calling a function func1() from main.I am would like to do following.
1) Inside func1(), I would like to assign 20 bytes to p using malloc method and later I would like to copy "Hello word " in to the string variable.
2) After function call ( func1()), I would like to print value that is in p variable.

How can I do this?


Regards,
Joy

推荐答案

pwasser [ ^ ]完美地回答了你的问题。

只是为了加入它，因为你也提到了C ++。



在C ++中，你可以也用更清晰的语法做到这一点 -

pwasser[^] has answered your question perfectly.
Just to add to it since you also mentioned C++.

In C++, you could also do this with a cleaner syntax -

int myfunc(char*& p)
{
	p = new char[20];

	strcpy(p, "Hello world");

	return 0;
}

int _tmain(int argc, _TCHAR* argv[])
{
	char* mypointer = NULL;
 
	myfunc(mypointer);
 
 	cout << mypointer << endl;
 
	delete [] mypointer;

	return 0;
}

使用malloc和new的示例（目前已注释掉）。

Example using both malloc and new (commented out at present).

#include "stdafx.h"
#include <iostream>


using namespace std;

int myfunc(char **p)
{
	//*p = new char[20];
    *p = (char*) malloc (20);

	strcpy(*p, "Hello world");

	return 0;
}

int _tmain(int argc, _TCHAR* argv[])
{
	char * mypointer = NULL;

	myfunc( &mypointer);

 	cout << mypointer << endl;

//	delete [] mypointer;
	free(mypointer);
 
  return 0;

}

malloc和free一起使用，新增和删除。对malloc使用delete会导致未定义的行为。

malloc and free are used together as are new and delete. Using delete with malloc results in undefined behaviour.

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