Going to give an exam 6 hours later dont understand a lecture code

what does this mean?

Code:

---

char strg1[] = “Engineering Problem Solving:”;
  char strg2[] = “fundamental Concepts”, strg3[50];

  strncpy(strg3, strg1, strlen(strg1)+1);
/*copy strlen+1 characters*/
  /*if enough room*/
  if (strlen(strg1)+strlen(strg2) < strlen(strg3)
    {
  strncat(strg3, strg2, strlen(strg2)+1);
  }
  char strg1[] = “Engineering Problem Solving:”;
  char strg2[] = “fundamental Concepts”, strg3[50];

  strncpy(strg3, strg1, strlen(strg1)+1);
/*copy strlen+1 characters*/
  /*if enough room*/
  if (strlen(strg1)+strlen(strg2) < strlen(strg3)
    {
  strncat(strg3, strg2, strlen(strg2)+1);
  }

---

Despite their names, strncpy() and strncat() were not designed to be used with strings.
I suggest you do not use them.

Also your string delimiters are not part of the Basic character set and are a syntax error.

Your ifs are never going to be true.

You cannot define the same identifier more than once.

Quote:

---

Originally Posted by qny

Despite their names, strncpy() and strncat() were not designed to be used with strings.
I suggest you do not use them.

---

I don't know where you could possibly have got this impression from - these functions work with null-terminated char arrays. In C, this is a string.

All the code is trying to do is to copy strg1 into strg3, and append strg2.

However, the way it does it will not work. Whoever wrote that code does not understand how C string functions work.

The strlen(strg1)+1 or strlen(strg2)+1 as third argument to strncat() and strncpy() respectively is silliness, as both functions will stop (at the zero terminator), and that occurs before strlen()+1 characters are copied.

The "if (strlen(strg1) + strlen(strg2) < strlen(strg3))" will always test false, since it comes immediately after the statement "strncpy(strg3, strg1, strlen(strg1)+1)" which will - as a side effect - ensure strlen(strg1) and strlen(strg3) are equal.

What the code therefore actually does is copy the string strg1 to strg3. Nothing more, nothing less.

(I'm assuming the code being repeated twice is a copy/paste error when posting).

Quote:

---

Originally Posted by qny

Despite their names, strncpy() and strncat() were not designed to be used with strings.
I suggest you do not use them.

---

Smoking the whacky tabacky tonight, eh?

But strncpy does not always append a \0, so the result might not be a proper C-string, in the traditional sense.

Quote:

---

Originally Posted by JohnGraham

I don't know where you could possibly have got this impression from - these functions work with null-terminated char arrays. In C, this is a string.

---

Unlike "proper string functions" they also work with non null-terminated char arrays.

Code:

---

char a[12] = "not a string";
char b[18] = "another non-string";
char c[] = "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"; /* 42 X's; c is a string */
strncpy(c + 3, a + 4, 5); /* c is "XXXa strXXX..." */
strncat(c, b + 2, 3); /* c is "...XXXoth" */

---

Quote:

---

Originally Posted by qny

Unlike "proper string functions" they also work with non null-terminated char arrays.

---

Well, the destination of strncat() must be null-terminated, meaning at least one of its parameters needs to be a string in order to use it properly.

And anyway, just because a function works with things other than what it's intended to is a very strange reason indeed to prompt someone specifically not to use them for what it's intended. I have a wrench that can also be used to hit people on the head - would you suggest I not use it for its normal purpose?

Quote:

---

Originally Posted by Salem

But strncpy does not always append a \0, so the result might not be a proper C-string, in the traditional sense.

---

strncpy(x, y, len) always copies a '\0' from y when len exceeds strlen(y) - which is what the code shown by the OP does.