Thread: string comparing

I can’t get my head around this problem. In the following code I want to enter a string that is a filename, for example hello.txt, myprog.bin assuming that they both exist on my c drive. However I want the program to accept .bin, .txt files only. If you don’t enter the 2 extensions I mentioned an error is displayed. Im unsure on how to do the decision making part with the file extensions. I think there should be a for loop to loop around string or strcpy command used within the program to compare extensions but not to sure. I’ve attached a piece of code that relates to it. Any help would be grateful.


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

main()
{
char string[10];
int result;

printf("Enter filename : "); //enter filename - example hello.txt would be valid
gets(string); //get file name


if (string != //unfinished here, unsure how to test condition
printf("Limit your entries to .bin, .txt extensions only"); //error message
else
printf("You entered %s with the correct extension\n", string); //otherwise prints correct text to screen
getch();
}

I was playing with your code, and to my shock, I couldn't get it to work, here's what I've got.

Code:

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


int getStringLength(char inputString[BUFSIZ])
{
 int i = 0;
 do
 {
  i++;
 }
 while(inputString[i]);
 return i;
}

int validExtension(char fileName[BUFSIZ])
{
 int fileLength = getStringLength(fileName);	

 char goodext1[4] = ".txt";
 char goodext2[4] = ".bin";
 char extension[4];
 extension[0] = fileName[fileLength-4];
 extension[1] = fileName[fileLength-3];
 extension[2] = fileName[fileLength-2];
 extension[3] = fileName[fileLength-1];

 printf("%s",extension);
 if(strcmp(goodext1,extension) || strcmp(goodext2,extension))
 {
  return 0;
 }
 else
 {
  return -1;
 }
}

int main(void) 
{ 
char string[BUFSIZ]; 
int result; 

printf("Enter filename : "); //enter filename - example hello.txt would be valid 
gets(string); //get file name 


if (!validExtension(string))  
printf("Limit your entries to .bin and .txt extensions only"); //error message 
else 
printf("You entered %s with the correct extension\n", string); //otherwise prints correct text to screen 
getch(); 
return 0;
}

nope that ain't the problem..

yeah but then if it's called a.txt.exe ...

if they try to open "hello.txt description.exe", it will think it is correct, it should only test the last 4 chars

Brian,

One thing I noticed:

Code:

char goodext1[4] = ".txt";
char goodext2[4] = ".bin";

You are writing beyond these two char arrays. They should both be declared as having 5 chars instead of 4.

Another thing:
You are treating "extension" as if it is null terminated, which it is not.

Code:

 extension[0] = fileName[fileLength-4];
 extension[1] = fileName[fileLength-3];
 extension[2] = fileName[fileLength-2];
 extension[3] = fileName[fileLength-1];

 printf("%s",extension);
 if(strcmp(goodext1,extension) || strcmp(goodext2,extension))
 ....

Either declare extension as "char extension[5]" and add a null "extension[4] = '\0' "
-or-
printf("%4.4s", extension) and use strncmp's instead of strcmp's

You need to also use && instead of || since one of the strcmp's will return a 1 if the other returns a 0.

Hope this helps.