Can I concatenate numeric constant with string in C?

Question

I have a very simple program, that is expected to take X characters of less from the user and print them back:

#include <stdio.h>
#define MAX_INPUT_LENGTH 8
#define HOME 1

int main()
{
    char vstup[MAX_INPUT_LENGTH];

    printf("Write something. But no more than "MAX_INPUT_LENGTH" characters.\n");
    scanf("%"MAX_INPUT_LENGTH"s", vstup);
    printf(vstup);


    system("pause");
    return 0;
}

Of course, my attempt with "blah"CONSTANT"blah" does not work. But there should be away to do it, shouldn't it? I thought constant are mostly just replaced pieces of text in the program, with only some basic logic.

I found an answer, it just had different title than I would expect: http://stackoverflow.com/questions/5459868/c-preprocessor-concatenate-int-to-string. I wonder if I'll get helpful flag for voting to close my own question. — Tomáš Zato, Apr 23 '14 at 17:22
Just in case you've wondered, there is no helpful point for flaging own questions. — Tomáš Zato, Apr 23 '14 at 19:05

R Sahu · Accepted Answer · 2014-04-23T17:35:36.413

7

This works for me.

#include <stdio.h>

#define STR2(a) #a
#define STR(a) STR2(a)

#define MAX_INPUT_LENGTH 8

int main()
{
   char vstup[MAX_INPUT_LENGTH+1];

   printf("Write something. But no more than " STR(MAX_INPUT_LENGTH) " characters.\n");
   scanf("%" STR(MAX_INPUT_LENGTH) "s", vstup);
   printf("%s\n", vstup);

   return 0;
}

edited Apr 23 '14 at 17:35

answered Apr 23 '14 at 17:29

R Sahu

204,454
14
159
270

@user3386109 Good observations. I fixed the answer. – R Sahu Apr 23 '14 at 17:35
+1. Two levels of macros are needed to stringify the argument of a function-like macros. – ajay Apr 23 '14 at 17:37
@RSahu +1 The string concatenation is a clever solution. – user3386109 Apr 23 '14 at 17:38

score -1 · Answer 2 · answered Apr 23 '14 at 18:29

-1

This is my version:

int max;
char frmt[10];

memset( frmt, 0, sizeof( frmt ) );

printf( "Enter a number:" );
scanf( "%d", &max );

char vstup[max];

printf( "Write something. But no more than %d characters.\n", max );

frmt[0] = '\%';
sprintf( frmt + strlen( frmt ), "%ds", max );

scanf( frmt, vstup );
printf( vstup );

answered Apr 23 '14 at 18:29

szpal

647
9
27

There is not much sense, but it use really dynamic format. – szpal Apr 23 '14 at 18:44

Can I concatenate numeric constant with string in C?

2 Answers2