Array of Pointer and call-by-reference - c++

Question

I have a little problem with a few simple lines of code.
Following lines I used to call my method:
char** paras = new char*;
inputLength = charUtils::readParameterFromConsole(paras, paraCount, stringBeginningIndex);
The method looks like following:
int charUtils::readParameterFromConsole(char** &inputs, int &paraCount, int &stringBeginningIndex) {
char input[BUFFER_STRING_LENGTH];
cin.getline(input, BUFFER_STRING_LENGTH);
if(strlen(input) > 0)
{
bool stringBeginning = false;
char* part = "";
string partString = "";
for(int i = 0; i < paraCount; i++)
{
if (i == 0)
part = strtok(input, " ");
else
part = strtok(NULL, " ");
inputs[i] = part;
}
} else
{
cout << "Error! No Input!" << endl;
}
cout << &inputs[0] << endl;
cout << inputs[0] << endl;
return strlen(input);
}
In the method readParameterFromConsole are the values correct, but in the calling method they aren't correcy any longer.
I am facing that problem since I refactored the code and make an new class.
Can anyone give me an advice please?

Answer 1

You are passing back pointers into a stack allocated variable, input when you say inputs[i] = part, because part is a pointer into input handed back by strtok.
http://www.cplusplus.com/reference/clibrary/cstring/strtok/

Answer 2

Your code as I'm writing this:
int charUtils::readParameterFromConsole(char** &inputs, int &paraCount, int &stringBeginningIndex) {
char input[BUFFER_STRING_LENGTH];
cin.getline(input, BUFFER_STRING_LENGTH);
if(strlen(input) > 0)
{
bool stringBeginning = false;
char* part = "";
string partString = "";
for(int i = 0; i < paraCount; i++)
{
if (i == 0)
part = strtok(input, " ");
else
part = strtok(NULL, " ");
inputs[i] = part;
}
} else
{
cout << "Error! No Input!" << endl;
}
cout << &inputs[0] << endl;
cout << inputs[0] << endl;
return strlen(input);
}
A main problem is that you're setting inputs[i] = pointer into local array. That array doesn't exist anymore when the function returns. Undefined behavior if you use any of those pointers.
As I understand it you want an array of "words" as a result.
That's easy to arrange (note: code untouched by compiler's hands):
#include <vector>
#include <string>
#include <sstream>
#include <stdexcept>
bool throwX( char const s[] ) { throw std::runtime_error( s ); }
typedef std::vector<std::string> StringVector;
std::string lineFromUser()
{
std::string line;
std::getline( cin, line )
|| throwX( "lineFromUser failed: std::getline failed" );
return line;
}
void getWordsOf( std::string const& s, StringVector& result )
{
std::istringstream stream( s );
std::string word;
StringVector v;
while( stream >> word )
{
v.push_back( word );
}
result.swap( v );
}
StringVector wordsOf( std::string const& s )
{
StringVector result;
getWordsOf( s, result );
return result;
}
// Some call, like
StringVector const words = wordsOf( lineFromUser() );
Again, this is off the cuff code, please just correct any syntax erors.
Cheers & hth.,