Good methods for converting char array buffers to strings?

Question

I am relatively new to C++. Recent assignments have required that I convert a multitude of char buffers (from structures/sockets, etc.) to strings. I have been using variations on the following but they seem awkward. Is there a better way to do this kind of thing?

#include <iostream>
#include <string>

using std::string;
using std::cout;
using std::endl;


char* bufferToCString(char *buff, int buffSize, char *str)
{
    memset(str, '\0', buffSize + 1);
    return(strncpy(str, buff, buffSize));
}


string& bufferToString(char* buffer, int bufflen, string& str)
{
    char temp[bufflen];

    memset(temp, '\0', bufflen + 1);
    strncpy(temp, buffer, bufflen);

    return(str.assign(temp));
}



int main(int argc, char *argv[])
{
   char buff[4] = {'a', 'b', 'c', 'd'};

   char str[5];
   string str2;

   cout << bufferToCString(buff, sizeof(buff), str) << endl;

   cout << bufferToString(buff, sizeof(buff), str2) << endl;

}

Answer 1

Given your input strings are not null terminated, you shouldn't use str... functions. You also can't use the popularly used std::string constructors. However, you can use this constructor:

std::string str(buffer, buflen): it takes a char* and a length. (actually const char* and length)

I would avoid the C string version. This would give:

std::string bufferToString(char* buffer, int bufflen)
{
    std::string ret(buffer, bufflen);

    return ret;
}

If you really must use the C-string version, either drop a 0 at the bufflen position (if you can) or create a buffer of bufflen+1, then memcpy the buffer into it, and drop a 0 at the end (bufflen position).

Answer 2

If the data buffer may have null ('\0') characters in it, you don't want to use the null-terminated operations.

You can either use the constructor that takes char*, length.

char buff[4] = {'a', 'b', 'c', 'd'};
cout << std::string(&buff[0], 4);

Or you can use the constructor that takes a range:

cout << std::string(&buff[0], &buff[4]); // end is last plus one

Do NOT use the std::string(buff) constructor with the buff[] array above, because it is not null-terminated.

Answer 3

std::string to const char*:

  my_str.c_str();

char* to std::string:

  string my_str1 ("test");
  char test[] = "test";
  string my_str2 (test);

or even

  string my_str3 = "test";