Left trim a char*

[paprica]

Hello.
What is wrong with my code?

#include <iostream>

using namespace std;

void trim(char *a)
{
	while(isspace(*a))
		a++;
}


int main()
{
	char *a = "    asdasd";

	trim(a);

	cout << a << endl;

	return 0;
}

" asdasd" is still displayed.