a simple c++ concatenate/split string and integer in a char array

Question

I am new to C++ programming. I have a string and an integer and I want to merge them into one char array and after that I want to split it and get the string and the integer. I worked a piece of code and it almost works. The only problem is that it sometimes creates some garbage at the end of the string. I searched this forum but I didn't get a suitable solution. What am I doing wrong? Is there a simpler solution? Thank you in advance. Here is my code:

#include <iostream>
#include <fstream>
#include <string.h>
#include <stdlib.h>
using namespace std;

int main() {
    cout << "string: ";
    char my_string[64];
    cin >> my_string;
    int i = 666;
    char i_size[8];
    sprintf( i_size, "%9d", i );
    strcat( my_string, i_size );
    cout << my_string << endl;
    char temp1[9] = { 0 };
    strncpy( temp1, my_string + ( strlen( my_string ) - 9 ), 9 );
    int in = atoi( temp1 );
    cout << "int = " << in << endl;
    char temp2[strlen( my_string ) - 9];
    strncpy( temp2, my_string, strlen( my_string ) - 9 );
    cout << "string = " << temp2 << "|" << endl;
    return 0;
}

And here is the output:

[corneliu@localhost prog-build]$ ./prog
string: e
e      666
int = 666
string = e|
[corneliu@localhost prog-build]$ ./prog
string: wewewewe
wewewewe      666
int = 666
string = wewewewe�@|
[corneliu@localhost prog-build]$

Your code uses C functions and C headers. These are considered non-idiomatic C++ and should be avoided. — Bartek Banachewicz
– Bartek Banachewicz, Commented Sep 18, 2013 at 13:04
Just a first glance: cin >> my_string; this is UNSAFE. Either specify the maximum amount to read via cin >> setw(64) >> my_string; (via <iomanip>) or even better: use a std::string from <string>. (Oh, and there are more of them: sprintf and strcat.) — dyp
– dyp, Commented Sep 18, 2013 at 13:05
char temp2[strlen( my_string ) - 9]; this -- variable length arrays -- is a gcc extension, or C99, or C++1y, but not currently allowed in C++ (98/03/11). Even in C++1y, I'd rather say it's not recommended. Either std::string or std::vector or even new char[strlen(my_string)-9] should be better. — dyp
– dyp, Commented Sep 18, 2013 at 13:13
I guess the actual problem comes from this: char temp2[strlen( my_string ) - 9];. It seems to me the space for the terminating \0 is missing in the array. Note: strncpy does not terminate the destination with a \0 if the buffer is too small. — dyp
– dyp, Commented Sep 18, 2013 at 13:18

Teh Suu · Accepted Answer · 2013-09-18 14:08:51Z

1

Your working with fixed sizes and if they are larger then 7 chars in your case, it will produce garbage.

Guess since you want to code in C++, you should stay away from C "string-functions"

#include <iostream>
#include <string>

using namespace std;
void main( ... )
{
   int my_int = 666;
   cout << "string: ";
   string my_string;
   cin >> my_string;

   // concat - separated by semicolon in this example
   stringstream ss;
   ss << my_string << ";" << my_int;

   cout << "string and int in one string: "
         << ss.str().c_str() << endl;

   // split
   string tmpStr = ss.str();
   size_t found = tmpStr.find(";");
   while( found != string::npos  )
   {
      cout << tmpStr.substr(0, found).c_str() << endl;
      tmpStr = tmpStr.substr( found+1 );
      found = tmpStr.find(";");

      // this case is true for the last part
      if( found == string::npos )
         cout << tmpStr.c_str() << "\n";
   }

   return 0;
}

Depending on what you want to do with it you may need to try to convert each string-parts to an integer and if it fails you know its a string otherwise you can assign it to an integer.

I think, even this approach is not what i would really do in productive code, it should give you a hint how to do what you want to do from there.

edited Sep 18, 2013 at 14:08

answered Sep 18, 2013 at 13:53

Teh Suu

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3 Comments

dyp Over a year ago

Also, if you include <string>, it shouldn't be necessary to use c_str() if you want to output a std::string via an ostream.

Teh Suu Over a year ago

yeah @DyP i forgot, "bad habit" to always use wcout since in most of my projects due to unicode support we only use wcout :P Always thought (w)cout doesn't like strings only chars... but didn't compile this have no proper enviroment atm

dyp Over a year ago

You can always use an online (www) compiler, like this one or that one. Insertion and extraction operators for string are defined in the header <string>.

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