Thread: Concatenation using system()

Hi there. Im having some problems with string concatenation.

The command in windows is:
ren c:\temp\text.txt text2.txt

But the number "2" i want to be a variable so i can change after i get this working.

Code:

main()
    {
    char var[] = "2";

    system("ren C:\\temp\\test.txt text + var[] + .txt");
  
    }

Any help? =)

Thx!

Lookup strcat and strncat

strcat - C++ Reference

Tim S.

sprintf() (or the safer snprintf() if you have it) is a cleaner way to achieve this.

Originally Posted by julianenepom

Yes!
Its working! Thanks Stahta01!

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main ()
{
  char var[] = "2";
  char str[80];
  strcpy (str,"ren C:\\temp\\text.txt text");
  strcat (str, var );
  strcat (str,".txt");
  puts (str);
  system(str);
  system("pause");
  
  return 0;
}

Of course you could also do this...

Code:

#include <stdio.h>
#include <string.h>

int main (void)
  { char fname[260];  
    int seq = 2;  

    sprintf(fname,"text%d.txt",seq);
    rename("c:\\temp\\text.txt", fname);

    return 0; }

... since C has a rename() function in it's libraries there's no reason to call system.
(Well, unless you're experimenting with system() calls, that is)

Well, now i cant do some other stuff...

In this code, the file text.txt is beeing deleted.

Code:

#include <stdio.h>
#include <string.h>

int main (void)
  { char fname[260];  
    int seq = 2;  

    sprintf(fname,"text%d.txt",seq);
    rename("c:\\temp\\text.txt", fname);

    return 0; }

The code I uded is ok, but Im getting this problem when I added "scanf":

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main ()
{
  char var[] = "";
  char str[80];

  scanf("%c", &var);

  strcpy (str,"ren C:\\temp\\text.txt text");
  strcat (str, var );
  strcat (str,".txt");
  puts (str);
  system(str);
  system("pause");
  
  return 0;
}

If I put the number 632, the result is something like 6♂².

Dont know what is happening... =P

Originally Posted by Salem

> char var[] = "";
The minimum length of a string, assuming you want to append anything other than just \0 (a no-op) is 2 characters.

char var[2] = "";
scanf( "%c", &var[0] );

But if you type in say 632, you need a longer string to being with.

Yea. The input size is 8. I will try it here.

Thx

Ok. The error that I get is:
When I try to Input a date like "20110420" using scanf, it gets only the first number, that is "2".

The code is:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main ()
{
  char var[8] = "";
  char str[80];

  scanf( "%c", &var[0] );

  strcpy (str,"ren C:\\temp\\text.txt text");
  strcat (str, var );
  strcat (str,".txt");
  puts (str);
  system(str);
  system("pause");
  
  return 0;
}

I think its a problem in the variable, but i really cant see what Im doing wrong... =P

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main ()
{
  char var[8] = "";
  char str[80];

  scanf( "%s", &var[0] );

  strcpy (str,"ren C:\\temp\\text.txt text");
  strcat (str, var );
  strcat (str,".txt");
  puts (str);
  system(str);
  system("pause");
  
  return 0;
}

The snippet below you are getting a single character.

Code:

scanf( "%c", &var[0] );

If you want to get a character string you would use:

Code:

scanf("%s",var);

Also don't forget to allow for the end of string character. You have defined your C-string having room for 7 characters plus the end of string but you want to input 8 characters so your array should be at least 9 characters.

Jim

Originally Posted by julianenepom

In this code, the file text.txt is beeing deleted.

Code:

#include <stdio.h>
#include <string.h>

int main (void)
  { char fname[260];  
    int seq = 2;  

    sprintf(fname,"text%d.txt",seq);
    rename("c:\\temp\\text.txt", fname);

    return 0; }

Ahhh... my bad. I don't use rename() very often and it turns out it needs the full path both times. Your file wasn't being deleted it was being moved to the folder the program is in (i.e. the current working directory). Try it like this...

Code:

#include <stdio.h>
#include <string.h>

int main (void)
  { char fname[260];  
    int seq = 2;  
   
    sprintf(fname,"C:\\temp\\text%d.txt",seq);
    printf("%s",fname);
    rename("C:\\temp\\text.txt", fname);
    return 0; }

Thanks all!! Its working! =)