Styjun

This program is supposed to take a user's input on an area code, search a separate file that has a bunch of phone numbers listed in the txt file, and a function search is supposed to test the phone number with the input area code to see if it matches. The main function then writes the phone numbers into a separate txt file.

I have tried to use strstr but I figured the best way to test it is to use strtok and strcmp, which is what I have now.

/* This program will search phone_numbers.txt for phone numbers. It will create a new file with unique area codes in each file.
 (Ex: 813 area codes will go into 813_phone_numbers file).
 --Brandon Yates
*/

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

int search(char *area_code, char *phone_number);
int read_line(char *str, int n);

int main() 
 char area_code[3];
 char phone_number[101];
 char *file_name;
 FILE *number_file;
 FILE *new_file;

 printf("Enter the area code: ");
 scanf("%s", &area_code);
 //area_code = &ac;
 read_line(area_code, 2);

 number_file = fopen("phone_numbers.txt", "r");
 if (number_file == NULL) 
 printf("Cannot open file.n");
 return -1;
 

 new_file = fopen("dest_file.txt", "a");
 if (new_file == NULL) 
 printf("Cannot open file.n");
 return -1;
 

 //scat = strcat(area_code, file_name);

 while (fgets(phone_number, sizeof(phone_number), number_file) != NULL && !feof(number_file) && !ferror(number_file)) 
 if (search(area_code, phone_number))
 fputs(phone_number, new_file);
 

 fclose(number_file);
 fclose(new_file);

 printf("Output: encoded words are written to file %s", file_name);

 return 0;


/*
 Search function determines if a phone number in the input file
 matches the area code.

 Search function returns 1 if the phone number matches the area code
 and 0 otherwise.
*/
int search(char *area_code, char *phone_number) 
 printf("testing");
 char *pch;
 pch = strtok(phone_number, "()");
 while (pch != NULL) 
 if (strcmp(area_code, phone_number) == 0)
 return 1;
 pch = strtok(NULL, "()");
 
 return 0;


int read_line(char *str, int n) 
 int ch;
 int i = 0;

 while ((ch = getchar()) != 'n') 
 if (i < n) 
 *str++= ch;
 i++;
 
 
 *str = ''; /* terminates string */
 return i; /* number of characters stored */

I expect the phone numbers to be written to a text file, but I end up with an empty file. What is going on?

There are multiple problems in your program:

• the array area_code is too small: it can only accommodate strings of 0, 1 or 2 characters. Since you do not tell scanf() to limit the input to a maximum of 2 characters, the area code typed by the user fills the array and scanf modifies memory beyond the end of the array, causing undefined behavior.



• 
  

  you read user input twice into the area_code array. The first time with scanf(), which may cause undefined behavior, but leaves the newline pending in standard input, and then with read_line() which reads the pending newline and makes area_code an empty string...

  
  
  

  Make area_code larger and either tell scanf() about the maximum number of characters to store there or just use read_line():

  
  
  

   char area_code[10];
   ...
   if (scanf("%9s", area_code) != 1)
   return 1;
  

  
  



• Note also that fgets(phone_number, sizeof(phone_number), number_file) != NULL && !feof(number_file) && !ferror(number_file) is redundant: fgets() will return NULL on error and/or end of file, no need to perform redundant tests.



• 
  

  The test in search is incorrect: if (strcmp(area_code, phone_number) == 0) you should instead compare the token with area_code:

  
  
  

   if (strcmp(area_code, pch) == 0)
  

  
  



• read_line also has a potential problem: its argument is the maximum number of characters to read, which is different from the argument to fgets() which is the size of the destination array. This is confusing and might cause bugs later if the function is given sizeof area_code for the size argument.