sprintf format specifier replace by nothing

Question

I am currently wondering if there is a way to replace the format specifier %u by nothing using sprintf

My question is about the use of a ternary operator in sprintf which gonna replace %u by a value or by nothing.

Here is an example of what I am trying to do :

int main (void)
{
   char mytab[10]={'\0'};
   uint_32 i=0;

   scanf("%u",&i);

   sprintf(mytab, "\"%u"\",i>0?i:/*Here is the syntax I want to find if it exists*/);
   printf("%s\r\n",mytab);

   return 0;
}

The result of the code I am trying to get is for example "1" if the input is 1 (or "2" if the input is 2...) and "" if the input is 0.

Do you have any ideas or explantion about it ? Thanks by advance.

Answer 1

我认为您应该将三进制运算符放在格式字符串上，根据i的值选择使用"%u"或"" 。

sprintf(mytab, i? "\"%u\"" : "\"\"", i);

Answer 2

Modify this statement

sprintf(mytab, "\"%u"\",i>0?i:/*Here is the syntax I want to find if it exists*/);  

This is what you need.

 (i>0)? sprintf(mytab, "%u",i) : sprintf(mytab,"%s","") ;

EDIT

AS H2CO3 suggested

You can also Use in this way.

if (i > 0)  
sprintf(mytab, "%"PRIu32, i); 
else
sprintf(mytab,"%s","");   

Also note that %u is not the appropriate format specifier for uint32_t , use "%"PRIu32

(i>0)? sprintf(mytab, "%"PRIu32,i) : sprintf(mytab,"%s","") ;  

Answer 3

I think a simple if statement is still the cleanest option:

char mytab[10] = "\"\"";

if (n > 0) {
    snprintf(mytab, sizeof mytab, "\"%" PRIu32 "\"", n);
}

Answer 4

You might (not?) like to use this dirty trick ^*1 (which makes gcc yell out warnings):

char mytab[11] = ""; 
uint32_t i = 0;
int result = scanf("%"SCNu32, &i);

if (1 != result)
{
  if (-1 == result)
  {
    if (errno)
    {
      perror("scanf() failed");
    }
    else
    {
      fprintf(stderr, "EOF reached\n");
    }
  }
  else
  {
    fprintf(stderr, "invalid input\n");
  }
}

sprintf(mytab, i>0 ?"%"PRIu32 :"%s", i>0 ?i :"");
printf("%s", mytab);

^{*1 To mention this explicitly: "dirty" in this context is a hint that this might invoke the fabulous Undefined Behaviour. So don't do this in prodcution!}

---

The sane apporach would be to do:

...

if (i)
{
  sprintf(mytab, "%"PRIu32, i);
}
printf("%s", mytab);

Please note that although the maximum number of digits for an unsigned 32bit number in decimal format is 10, you still need to reserve one character for the 0 -terminator.