Question about using sprintf() to concatenate C-strings

Projects Programming
1

You guys are mean. You make me do my own research.
Thank you.

Furthering my progress away from String class to C-strings

I want to turn a U.S. phone number into a readable number.
For example, turn "19785551212" into "1-978-555-1212" for human reading.

This code works as expected. Is there a better way to parse a C-string or have I properly figured it out?

void setup() {
  Serial.begin(115200);
  Serial.println();
  Serial.println();


  //--------------------------------
  //--- Parse the phone number -----

  char areaCode[4];   // 978
  char prefix[4];     // 555
  char phone[5];      // 1212

  char str1[] = "19785551212";            //Starting here...
  char str2[40];                          //Holds the formatted phone number
  char str3[4];                           //Area code 978
  char str4[4];                           //Prefix    555
  char str5[5];                           //Phone     1212

  strncpy ( str3, str1 + 1, 3 );          //Area code, 3 characters
  str3[3] = '\0';
  strncpy ( str4, str1 + 4, 3 );          //Prefix, 3 characters
  str4[3] = '\0';
  strncpy ( str5, str1 + 7, 4 );          //Phone, 4 characters
  str5[4] = '\0';

  sprintf(str2, "1-%s-%s-%s", str3, str4, str5);
  Serial.println(str2);


}

void loop() {
}
2 
void setup() {
  Serial.begin(115200);
  char str1[] = "19785551212";
  char str2[40];
  sprintf(str2, "1-%.3s-%.3s-%.4s", str1 + 1,  str1 + 4, str1 + 7);
  Serial.println(str2);
}
void loop() {}

1-978-555-1212
3

Thanks- I am still learning my way around C-strings, I have a lot of String class to unlearn.

Looking at your suggested code drives home that str1 is just a pointer into the data in str1[]. So there is no need to parse each part separately.