Question

Let’s say I have a struct called test:

struct  test
{
    char name[16];

} test;

I want to read the user’s input and put it in the name field. Let’s say the user has typed in "hello" as the input. My code is like this:

struct test test1;

strcpy(test1.name, user_input);

Now the name has 5 characters in it ("hello"), but I want it to have its 16 characters: 5 for the actual input, and the rest white spaces. How can I achieve that?

Answer 1

sprintf() can do it:

sprintf(test1.name,"%-15s","John Doe");
printf("[%s] length of test1.name: %ld\n",test1.name,strlen(test1.name));
sprintf(test1.name,"%-*s",(int) sizeof(test1.name) - 1,"Jane Jones");
printf("[%s] length of test1.name: %ld\n",test1.name,strlen(test1.name))

output:

[John Doe       ] length of test1.name: 15
[Jane Jones     ] length of test1.name: 15

or

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

int copy_with_pad(char *destination,const char *source, int dest_size, char pad_char)
{
   int pad_ctr = 0;
   if (dest_size < 1 ) return -1;
   int source_length = strlen(source);
   int data_size = dest_size - 1;
   destination[data_size] = '\0';
   int i = 0;
   while (i < data_size)
   {
      if ( i >= source_length )
      {
         destination[i] = pad_char;
         pad_ctr++;
      }
      else
         destination[i] = source[i];
      i++;
   }
   return pad_ctr;
}


int main(void)
{
   struct test {
      char name[16];
   };
   struct test test1;
   int chars_padded = copy_with_pad(test1.name,"Hollywood Dan",
                                    sizeof(test1.name),' ');
   printf("%d padding chars added: [%s]\n",chars_padded,test1.name);
   chars_padded = copy_with_pad(test1.name,"The Honorable Hollywood Dan Jr.",
                                 sizeof(test1.name),' ');
   printf("%d padding chars added: [%s]\n",chars_padded,test1.name);
   chars_padded = copy_with_pad(test1.name,"",16,' ');
   printf("%d padding chars added: [%s]\n",chars_padded,test1.name);
}

output

2 padding chars added: [Hollywood Dan  ]
0 padding chars added: [The Honorable H]
15 padding chars added: [               ]