Notes

• C does not have print or I/O built-in
  • For strings and printing, use standard C libraries

printf()

• A function in the standard IO library
  • #include <stdio.h>

• The first argument is a format string.

• Characters in the format string are copied to standard output

• Format codes beginning with % reference arguments that come after the format string, in order

• Need to output a newline character '\n' to end a line

• printf format code:

  %d	Decimal integer (int)
  %x	Hex integer (int)
  %f	Floating number (float)
  %s	String (char * or char [1)
  %c	Character (char)
  %p	Pointer (for debugging)

• Example

  //prints —> Person: Dan GPA: 2.5
  printf(“Person: %s GPA: %f\n”, name, gpa);

string.h functions

#include <string.h>

strncpy() / strcpy()

strncpy() documentation

• strncpy() code

  /**
   * @brief Copy a string
   *
   * @param dest The destination buffer
   * @param src The source to copy from
   * @param n maximum number of bytes to copy
   * @return char* a pointer same as dest
   */
  char * my_strncpy(char * dest, const char * src, size_t n) {
      size_t index = 0;
      while (( * (src + index) != '\0') && (index < n)) {
          *(dest + index) = * (src + index);
          index++;
      }
      while (index < n) {
          *(dest + index) = '\0';
          index++;
      }
      return dest;
  }

strcpy() documentation

strlen()

Documentation

• Code

  /**
   * @brief Calculate the length of a string
   *
   * @param s a constant C string
   * @return size_t the number of characters in the passed in string
   */
  size_t my_strlen(const char * s) {
      size_t total = 0;
      int index = 0;
      while ( * (s + index) != '\0') {
          total++;
          index++;
      }
      return total;
  }

strncmp() / strcmp()

strncmp() documentation

• strncmp() code

  /**
   * @brief Compare two strings
   *
   * @param s1 First string to be compared
   * @param s2 Second string to be compared
   * @param n First (at most) n bytes to be compared
   * @return int "less than, equal to, or greater than zero if s1 (or the first n
   * bytes thereof) is found, respectively, to be less than, to match, or be
   * greater than s2"
   */
  int my_strncmp(const char * s1, const char * s2, size_t n) {
      size_t index = 0;
      while (index <= n) {
          if ( * (s1 + index) - * (s2 + index) == 0) {
              index = index + 1;
          } else {
              if ( * (s1 + index) - * (s2 + index) > 0) {
                  return 1;
              }
              return -1;
          }
      }
      return 0;
  }

strcmp() documentation

Questions & Answers

Practice question: a programmer is attempting to copy a string s1 into a buffer of characters s2. Can you spot the issue with the code below?

strncpy(s2, s1, strlen(s1));

• TA Answer

  • The third parameter should be “strlen(s1)+1” to account for the null terminating character at the end of the string