String Handling in C

In C, you can obtain the length of a string using strlen. However, each call to strlen takes $O(n)$ time. For applications that perform frequent string operations, this can easily become a performance bottleneck when strings are long—especially in high-traffic applications. One solution is to track the string length in a separate variable and update it whenever the string is modified. That way, retrieving the string length only requires reading this variable, bringing the time complexity down to $O(1)$.

Another thing to watch out for is that C makes no assumptions about your buffer size. You need to be very careful when performing operations like concatenation. For example, if you write:

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

int main(void) {
  char buf1[20] = "abc";
  char buf2[] = "def";
  strcat(buf1, buf2);
  printf("%s\n", buf1);
  return 0;
}

This code concatenates the contents of buf2 onto buf1. However, if we reduce the size of buf1 to 5:

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

int main(void) {
+ char buf1[4] = "abc";
  char buf2[] = "def";
  strcat(buf1, buf2);

  printf("%s\n", buf1);
  return 0;
}

Running this will result in an error. This happens because concatenating buf1 and buf2 exceeds a size of 4, leading to a buffer overflow. The solution is to check beforehand whether the combined string length will cause an overflow before performing the concat operation, and reallocate memory if it will.