In this instruction, we are going to walk you through how to get a substring in C without barely a headache being able to disturb your mind.

Reaching the destination faster with ultra fulfilled support from us on what is a substring as well as ways to find and copy it better. Let’s dig in!

What Exactly Is A Substring In C?

Not only in C programming but in any other software, a substring is basically a string belonging to another longer string.

Let’s say we have the string “programmer”, then “program”, “ram”, “” (content-free String), and so on would probably be a substring of such a term.

However, if you pick up “prom” from “programmer”, it is unlikely to be a substring. Instead, a subsequence would be better for you to attach rather than the first clumsy label.

How To Get A Substring In C

Utilizing The Strncpy() Function

Strncpy is a C string library function specified in the header file < String.h>. Its mission is to duplicate the number of bytes specified from the source string. Once the copy progress has been nailed, it’s time to head straight to the needed target.

Also, mark in mind that there are only three acceptable arguments for the strncpy to get your code successful, including a source pointer, a destination char*, and an integer indicating the number of bytes to copy.

So that we know if the number of bytes supplied exceeds the length of the source string, the destination stores extra null bytes.

What is more, because the strncpy function delivers a reference to the intended String, we may call it from the printf instruction to print the substring directly.

The following example shows how to print the first four characters of a substring, followed by the next ten characters.

Running the code

// string::substr

#include <iostream.h>

#include <string.h>

int main ()

{

  std::string str="We think in generalities, but we live in details.";

                                           // (quoting Alfred N. Whitehead)

  std::string str2 = str.substr (3,5); // "think"

  std::size_t pos = str.find("live"); // position of "live" in str

  std::string str3 = str.substr (pos); // get from "live" to the end

  std::cout << str2 << ' ' << str3 << '\n';

  return 0;

} 

Output

think live in details.

Utilizing The Memcpy() Function

The memcpy() method transfers the specified number of the given-in-advance characters from one memory location to another. The < String.h> actually also contains this method.

There is perhaps only one minus that whenever the destination and source locations are found the same, this function will cause certain bothersome issues. As such, this feature won’t be any help in checking for null addresses or seeing whether an overflow happens.

If things turn out well, the result of memcpy() will end up with a pointer denoting straight to the target string. Otherwise, there is also no such thing as returning a value to indicate errors.

Running the code

/* memcpy example */

#include <stdio.h>

#include <string.h>

struct {

  char name[40];

  int age;

} person, person_copy;

int main ()

{

  char myname[] = "Pierre de Fermat";

  /* using memcpy to copy string: */

  memcpy ( person.name, myname, strlen(myname)+1 );

  person.age = 46;

  /* using memcpy to copy structure: */

  memcpy ( &person_copy, &person, sizeof(person) );

  printf ("person_copy: %s, %d \n", person_copy.name, person_copy.age );

  return 0;

}

Output

person_copy: Pierre de Fermat, 46

Conclusion

It depends on your way of coding, so these two approaches above can be the best fit to get a substring in C. Now that we got your back with an extremely illustrative picture regarding this math, hopefully, you are no longer confused about figuring out the values needed.

Wait for no more but give a stab at it, and don’t forget to leave us comments telling us whether it works out well or not!