Pointers in functions

How do I pass a char pointer to a function and write it out. Somethings wrong with this code and I dont know why. Help?

  #include <iostream>

using namespace std;

// Function Decalarations
void Hello(char*);
// welcomeMessage - prints a welcoming message

char* myName;

int main()
{
	cin >> myName;
	Hello(myName);
	return 0;
}

// Function Definitions
void Hello(char* myName)
{
	cout << "HelloWorld! " << myName << endl;
}

jlb (4973)

Why is *myName global?

Where did you allocate memory for that pointer?

Why are you trying to pass myName into that function, when myName is global?

Why are you trying to pass a char* instead of just using std::string instead?

ne555 (10692)

$ g++ -W{all,extra,pedantic} foo.cpp -ggdb
$ gdb ./a.out
(gdb) run
Program received signal SIGSEGV, Segmentation fault.

(gdb) backtrace
#0  0x00007ffff7b44248 in std::basic_istream<char, std::char_traits<char> >& std::operator>><char, std::char_traits<char> >(std::basic_istream<char, std::char_traits<char> >&, char*) ()
   from /usr/lib/libstdc++.so.6
#1  0x000000000040091e in main () at foo.cpp:13

(gdb) frame 1
13 cin >> myName;

(gdb) print myName
$1 = 0x0

`myName' points to NULL. In the reading operation you are trying to dereference a NULL pointer.

#include <iostream>
#include <string>

void hello(const std::string &name);

int main(){
   std::string myName;
   std::cin >> myName; //it would not read spaces
   hello(myName);
}

void hello(const std::string &name){
   std::cout << "HelloWorld! " << name << std::endl;
}

Or if you do want to use char

void Hello(const char *name);
int main(){
   const int a_big_enough_number = 42;
   char myName[a_big_enough_number];
   std::cin >> myName;
   Hello(myName);
}

jlb (4973)

But if you do use the above solution with the char be sure to limit the number of characters that will be retrieved to avoid buffer overflow. And remember the extraction operator stops processing when it encounters as white space character.

1
2
3

#include <iomanip>
...
std::cin >> setw(a_big_enough_number - 1) >> myName;

novellof (210)

The problem is you are creating a pointer to a char that is not pointing to anything...

Allocate memory in the heap by using this ---> char* myName = new char;

You have to initialize it.

#include <iostream>

using namespace std;

// Function Decalarations
void Hello(char* );
// welcomeMessage - prints a welcoming message



int main()
{
    char* myName = new char;
    
    cout << "Enter Your name " << endl;
    
	cin >> myName;
    
	Hello(myName);
    
    
	return 0;
}

// Function Definitions
void Hello(char* myName)
{
	cout << "Your Name:  " << myName << endl;
}

Last edited on

patriic48 (100)

Thanx! Now I understand the code!

Regards / Patrik

ne555 (10692)

1
2
3

    char* myName = new char; //just 1 character
    cout << "Enter Your name " << endl;
    cin >> myName; //trying to read an string

remember that c-strings are zero terminated, ¿how big could be the string that you can read with that code?

Avilius (617)

Don't forget that you're only allocating space for one character.

Use this:

char* str = new char[size_of_string + 1];

// Do what you need to do
// ........

delete[] str; // Free memory after you're done using it

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