How to store strings that end with certain characters?

Question

I want to create a program that opens and writes to 3 different text files, the names a user inputs.

The condition would be that if last names end with certain characters, they would be saved to a specific text file.

For example, if the user inputs a last name that ends with ian it should be saved to the ARMENIA.TXT folder.

Here is my code and the issues I encounter with it:

struct names {
    char firstName[20];
    char lastName[30];
} person;

int main() {
    FILE *arm, *ita, *esp;
    char ian[] = "ian";
    char ini[] = "ini";
    char ez[] = "ez";
    char response;
    char *ret;

    arm = fopen("C:\\Programming\\ARMENIA.TXT", "wt");
    ita = fopen("C:\\Programming\\ITALIA.TXT", "wt");
    esp = fopen("C:\\Programming\\ESPANIA.TXT", "wt");

    if (arm, ita, esp == NULL) {
        printf("Error: The archives could not be created.");
        return 1;
    } else {
        printf("Operation Successful: Archives created.\n\n");
    }

    do {
        fflush(stdin);
        printf("\n\nPlease input your first name: ");
        scanf("%s", &person.firstName);
        printf("Please input your last name: ");
        scanf("%s", &person.lastName);

        if (ret = strstr(person.lastName, ian)) {  
            fwrite(person.lastName, 1, strlen(person.lastName), arm);
            fwrite(person.firstName, 1, strlen(person.firstName), arm);
        }

        if (ret = strstr(person.lastName, ini)) { 
            fwrite(person.lastName, 1, strlen(person.lastName), ini);
            fwrite(person.firstName, 1, strlen(person.firstName), ini);
        }

        if (ret = strstr(person.lastName, ez)) { 
            fwrite(person.lastName, 1, strlen(person.lastName), ez);
            fwrite(person.firstName, 1, strlen(person.firstName), ez);
        }

        printf("\n\nWould you like to enter another person into the archive?: (y) or (n): ");
        scanf(" %c", &response);

    } while (response == 'y');

    printf("\n\nThe operation has finished.\n\n");

    fclose(arm);
    fclose(ita);
    fclose(esp);

    return 0;
}

Issue: Will save to folder if last name contains ian (or ini / ez) in ANY part of the last name. How do I make the condition only if it ENDS with these strings?

Issue: Will crash if last name contains ini or ez -- basically, only first If statement works.

Issue: Needs to be saved as Lastname, Firstname -- For now, it saves as LastnameFirstname.

Answer 1

There are a number of unrelated issues here.

arm = fopen("C:\\Programming\\ARMENIA.TXT", "wt");

That should be "w+", not "wt". Same for the others. Or just "w", unless you want to both read and write.

if (arm, ita, esp == NULL)

The comma operator evaluates its left operand and discards it, then evaluates its right operand and keeps that value. So this is equivalent to if (esp == NULL)

fflush(stdin);

This is meaningless. When printing, the system is allowed to buffer output and then print it all at once, which can speed things up. fflush forces it to actually print anything that's currently in the buffer. It's useful if, for example, you want to prompt the user for input and need to make sure the prompt shows up.

As such, it only works on an output stream. (This error is actually taught in some terrible references, so I suspect this one isn't your fault. You should stop using whatever reference told you to do this.)

Addendum: As Olaf points out in the comments, this invokes undefined behavior, which is a topic unto itself. The short and imprecise version is that any undefined behavior creates bugs that are really hard to track down.

if (ret = strstr(person.lastName, ian)) 

This tells you that ian is in person.lastName somewhere, but not that it's at the end. For example, suppose the last name is "ian in ez". It'll match all three of your conditions. As an aside, you don't need to store ian in a variable; you can just do strstr(person.lastName, "ian").

Answer 2

In addition to the issues Ray pointed out, see the following simple code for a strEndsWith-function. Hope it helps.

int strEndsWith(const char* str, const char* ending) {
    size_t strlenStr = strlen(str);
    size_t strlenEnding = strlen(ending);
    if (strlenStr < strlenEnding)
        return 0;

    const char* strAtEnding = str + strlenStr - strlenEnding;

    return (strcmp(strAtEnding, ending) == 0);
}

Answer 3

Your program has multiple issues.

Some of the have been addressed by Ray and Stephen Lechner, but here are some more:

• The reason for the crashes is you pass string to fwrite instead of FILE* stream pointers: fwrite(person.lastName, 1, strlen(person.lastName), ini); should be written:

  fwrite(person.lastName, 1, strlen(person.lastName), ita);
  

  This is an indication that you compile without proper warnings enabled. Let the compiler help avoid such silly mistakes with -Wall for gcc or /W3 for msvc.

• Note also that you should use fprintf to properly format the output to your text files. For example:

  if (strEndsWith(person.lastName, "ian")) {
      fprintf(arm, "%s, %s\n", person.lastName, person.firstName);
  }
  

Here is an improved version:

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

int strEndsWith(const char *str, const char *ending) {
    size_t len1 = strlen(str);
    size_t len2 = strlen(ending);
    return len1 >= len2 && !strcmp(str + len1 - len2, ending);
}

int main(void) {
    FILE *arm = fopen("C:\\Programming\\ARMENIA.TXT", "wt");
    FILE *ita = fopen("C:\\Programming\\ITALIA.TXT", "wt");
    FILE *esp = fopen("C:\\Programming\\ESPANIA.TXT", "wt");

    if (arm == NULL || ita == NULL || esp == NULL) {
        printf("Error: The archives could not be created.\n");
        return 1;
    } else {
        printf("Operation Successful: Archives created.\n\n");
    }

    for (;;) {
        char firstName[20];
        char lastName[30];
        char response;

        printf("\n\nPlease input the first name: ");
        if (scanf("%19s", firstName) != 1)
            break;
        printf("Please input the last name: ");
        if (scanf("%29s", lastName) != 1)
            break;

        if (strEndsWith(lastName, "ian")) {  
            fprintf(arm, "%s, %s\n", lastName, firstName);
        }
        if (strEndsWith(lastName, "ini")) {  
            fprintf(ita, "%s, %s\n", lastName, firstName);
        }
        if (strEndsWith(lastName, "ez")) {  
            fprintf(esp, "%s, %s\n", lastName, firstName);
        }

        printf("\n\nWould you like to enter another person into the archive?: (y) or (n): ");
        if (scanf(" %c", &response) != 1 || response != 'y')
            break;
    }

    printf("\n\nThe operation has finished.\n\n");

    fclose(arm);
    fclose(ita);
    fclose(esp);

    return 0;
}