Programming

sprintf(dst, "%.*s", count, src + start);

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

main(){

int start = 3;
int stop  = 9;
const char src[] = "A test string";

// print 6 char from src+start 
printf("%.*s\n",stop-start, src + start);

// &src[3] == src+3
printf("%s %s\n", &src[3], src+3);

// what is src+start ?
printf("src + %d = %s\n",start,src+start);

// print nchar from src+start
int nchar = 9;
printf("%.*s\n",nchar, src + start);


}

$ gcc test2.c
$ ./a.out 
est st
est string est string
src + 3 = est string
est strin

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

main(){

int start = 3;
int stop  = 9;
const char src[] = "A test string";

// I confused from  variable "count" that whether you like to print "char-start to char-stop" '3 - 9' or n char from start ?
unsigned int count = stop - start;

// print 6 char from src+start 
printf("char %d-%d = %d ~ %.*s\n",start,stop,count,count, src + start);

// n char specified in stop from starting
printf("Total char %d from start ~ %.*s\n",stop,stop,src + start);


}

$ ./a.out 
char 3-9 = 6 ~ est st
Total char 9 from start ~ est strin

sprintf(dst, "%.*s", count, src + start);

char fmt[10];
sprintf(fmt, "%%.%ds", count);
sprintf(dst, fmt, src + start);

int sprintf(char *str, const char *format, ...);

sprintf(),  snprintf(),  vsprintf()  and vsnprintf() write to the character string str.
 One  can  also specify explicitly which argument is taken, at each place where an argument is required, by writing "%m$" instead of '%' and "*m$" instead of '*', 
where the decimal integer m denotes the position in the argument list of the desired argument, indexed starting from 1.  Thus,
           printf("%*d", width, num);    and     printf("%2$*1$d", width, num);  are equivalent.

sprintf(dst, "%.*s", count, src + start);

sprintf(dst, "%s %d", count, src + start);

sprintf(fmt, "%%.%ds", count);

warning: format ‘%c’ expects type ‘int’, but argument 2 has type ‘char *’ [-Wformat]
warning: format ‘%c’ expects type ‘int’, but argument 2 has type ‘size_t *’ [-Wformat] etc.

#include <stdio.h>
main(){
             printf("%*d\n", 5, 10); 
             printf("%.*d\n", 3, 10); 
             printf("%.*s\n", 3, "akshay");
      }

$ ./a.out 
   10
010
aks

#include <stdio.h>
main(){
           // Equal
           printf("%.*s\n", 3, "akshay");
           printf("%.3s\n", "akshay" );
      }

$ ./a.out 
aks
aks

#include <stdio.h>
main(){
          int count = 3;
          char fmt[10];
          char src[6] = "akshay";
          char dst[6];

          // Don's approach : following statements creates format that is
          // fmt will be "%.3s"
          sprintf(fmt, "%%.%ds", count);

          printf("Format is : %s\n", fmt);

          // following statement is equal to sprintf(dst,"%.3s",src)
          sprintf(dst, fmt, src);
          printf("output is : %s\n", dst);
      }

$ ./a.out 
Format is : %.3s
output is : aks

sprintf(fmt, "%%.%ds", count)