CODEWITHSUNDEEP
cstringchar
am3
am3

Reputation: 741

converting char to string using snprintf in C

I'm using the below code to convert an array of characters to a string C. However the output is different from what I expected. 

#include<stdio.h>
int main() 
{
    char data[5] = {
        'a', 'b', 'c', 'd', '\0'
    };
    char buff[100];
    int i = 0;

    while (data[i] != '\0')
    {
        printf("%c Character here \n", data[i]);
        snprintf(buff, 100, "%s", & data[i]);
        printf("%s String here\n", buff);
        i++;
    }
}

The result I expect is 

a Character here 
a String here
b Character here 
b String here
c Character here 
c String here
d Character here 
d String here

However I'm getting this as output 

a Character here 
abcd String here
b Character here 
bcd String here
c Character here 
cd String here
d Character here 
d String here

Can somebody explain this?

Upvotes: 0

Views: 1553

Answers (1)

Iskar Jarak
Iskar Jarak

Reputation: 5325

data is already a string, since it is a null-terminated sequence of characters (which is what a string is in C).

You are getting those results because you are calling snprintf inside a loop over data.

First you call snprintf() on &data[0], which copies data into your buffer from data[0] until it reaches the null. Then you call snprintf() on data[1], which copies into your buffer from &data[1] until it reaches the null. And so on...

And each time you do so, you call printf() on the buffer, with a %s parameter... which prints the argument as a sequence of characters until it reaches the terminating null (i.e. %s prints a string).

If you want to print a single character, use %c. If you want to print to the buffer character by character until you reach the null, do it manually - but snprintf() is designed so that you don't have to do that.

Using snprintf() in a more common manner:

#include<stdio.h>

int main() {
  char data[5] = {'a', 'b', 'c', 'd', '\0'};
  // or char data[] = "abcd";

  char buff[100] = {0};
  snprintf(buff, sizeof buff, "%s", data);
  printf("%s String here\n", buff);
  return 0;
}

Copy/print each character manually:

#include<stdio.h>

int main() {
  char data[5] = {'a', 'b', 'c', 'd', '\0'};
  // or char data[] = "abcd";

  char buff[100] = {0}; // initialises buff by filling it with zeroes

  char *ptr = data, *buff_ptr = buff;
  while (*ptr) {
    *buff_ptr = *(ptr++);
    printf("%s current\n", buff_ptr++);
    printf("%s from the start\n", buff);
  }
  return 0;
}

Upvotes: 7

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