Question

I am trying to copy a string which might contain null characters in the middle to a char array.
I have constructed the following function.

 void SaveStringToChar(string &mystring,const char * &ArrChar)
 {//begin function

   std::string str;
   char * writable = new char[str.size() + 1];
   std::copy(str.begin(), str.end(), writable);
   writable[str.size()] = '\0';
   ArrChar = writable;

 }//end function

my question is this method guarantees that I wont lose the characters after a null element.
and my other question is I get this linker error which I don’t know what it means.

/tmp/ccUpCRaz.o: In function `Parser::RuleParser(char const*)’:
Parser.cpp:(.text+0x3f6): undefined reference to Parser::SaveStringToChar(std::basic_string, std::allocator >&, char const*&)’
collect2: ld returned 1 exit status

anyhint please.

this is the function I pass things to compare.

  void Search( size_t TextLength, const char *Text, const vector<const char *> &patterns );

Answer 1

You need to define the function as a member of Parser::. It is currently defined as:

void SaveStringToChar(string &mystring,const char * &ArrChar)

Change to:

void Parser::SaveStringToChar(string &mystring,const char * &ArrChar)

The std::copy() will copy all the characters. However, the caller will not know how many characters ArrChar actually points to as functions like strlen() will stop counting at the first null character. You could change the signature of SaveStringToChar() to accept another argument size_t& ArrCharLen that would be populated with the number of characters in ArrChar. Of course, mystring will have the length of ArrChar so maybe you are already storing this prior to the call to SaveStringToChar().

EDIT (after vector<const char*> comment):

The true number of bytes is lost once the const char* is added to the vector. Why not use a vector<std::string> and you have std::string::length() to know how many characters there are actually stored in std::string.

EDIT2 (after comparison function .c_str() with text.length():

Instead of passing .c_str() and .length() to compare against elements in a vector<const char*> just pass the std::string to the compare function and compare against elements of a vector<std::string>: the std::string::operator==() will correctly compare strings will embedded null characters. You could then use std::find() to search the vector<std::string> for the std::string read from the file.