Need help concatentating 2 strings and an int.

[dissectcode2]

Hi - please help. I have two strings and a number which I need to concatenate together and I'm confused to what is the best approach. Here is my code:

char *s1 = "iamafilename_";
char *s2 = ".tif";

int i;
for( i = 0; i < 10; i++ )
{

 char itoaBuff[100];
 int num_len = sprintf(itoaBuff, "%s", i);

 char *f = (char *)malloc( (strlen(s1) + strlen(s2) + num_len) * sizeof(char) + 1 );

 strcat( f, s1 );
 strcat( f, itoaBuff );
 strcat( f, s2 );

 printf("the three strings concatenated is: %s\n\n", f);

 free( f );
       
}

i get a seg fault by the way. can anyone see what i am trying to do and advise me please?

[dissectcode2]

I wish I could delete this post because I realized my sprintf needed %d inside and it worked. I'm smarter than I thought. pat pat

[dissectcode2]

or would it have been better to use scanf ??

[weaknessforcats]

What I notice is:

strcat( f, s1 ); 
 strcat( f, itoaBuff ); 
 strcat( f, s2 );

strcat operates by appending after a \0 which your buffer f may not have. I suggest an initial strcpy then the strcats:

strcpy( f, s1 ); 
 strcat( f, itoaBuff ); 
 strcat( f, s2 );

or at least set f[0] to \0 before the strcats.

Without that initial \0 your strcat will append an indeterminate number of bytes. That could cause you to overrun f and corrupt memory.

[dissectcode2]

thank you weaknessforcats because i was going crazy with a seg fault, and thought it might have something to do with all strcat's, and you validated it with good info. now i know what is the correct approach.