Question on pointer to string variable

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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

Posted 10-Mar-14 1:48am

joyjhonson

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2 solutions

Solution 2

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 -

C#

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;
}

Posted 10-Mar-14 17:44pm

«_Superman_»

v2

Comments

[no name] 11-Mar-14 0:04am

Correct but I had included it also.

«_Superman_» 11-Mar-14 1:09am

I don't mean the usage of new and delete.
You can see the difference in how the myfunc function takes a reference to a char* and the syntactical differences because of that.

[no name] 11-Mar-14 1:12am

Indeed and OP did mention c++.

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User 59241 · Accepted Answer · 2014-03-10T02:00:00

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

C++

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

Question on pointer to string variable

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Question on pointer to string variable

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