comparing strings

[BrianJones]

I have a problem with the int strcmp(str1,str2) function:

When I do:

char *pass;
char *passv;

pass = getpass("Please enter.....");
passv = getpass("Please verify.....");

if(strcmp(pass,passv)==1) // i.e. failure{
cout<<"Verification failed!<<endl;
exit(1);
}

Problem: Does't seem to work properly, even though the strings, pass and
passv are exactly the same. for some reason, it doen't go in to the if
statement Any syggestions?

Cheers,
Ben

 

[Rolf Magnus]

I have a problem with the int strcmp(str1,str2) function:

When I do:

char *pass;
char *passv;

pass = getpass("Please enter.....");
passv = getpass("Please verify.....");

if(strcmp(pass,passv)==1) // i.e. failure{
cout<<"Verification failed!<<endl;
exit(1);
}

Problem: Does't seem to work properly, even though the strings, pass
and passv are exactly the same. for some reason, it doen't go in to
the if statement Any syggestions?

Yes, read your compiler's documentation about strcmp. strcmp returns a
number less than zero if the first string is 'less' than the second,
and greater than zero if the second string is 'less'. The exact value
is not specified. It might be 1 or 10 or 100, or it might depend on the
exact combination of strings you pass to strcmp. So comparing the
result to 1 is wrong. Write:

if (strcmp(pass, passv) != 0) ...

Another (better) idea would be to use strings. Change your getpass
function so that it returns a string and write:

std::string pass = getpass("Please enter.....");
std::string passv = getpass("Please verify.....");

if (pass != passv) // i.e. failure
{
cout<<"Verification failed!<<endl;
exit(1);
}

 

[Alf P. Steinbach]

* BrianJones:

I have a problem with the int strcmp(str1,str2) function:

When I do:

char *pass;
char *passv;

pass = getpass("Please enter.....");
passv = getpass("Please verify.....");

if(strcmp(pass,passv)==1) // i.e. failure{
cout<<"Verification failed!<<endl;
exit(1);
}

Problem: Does't seem to work properly, even though the strings, pass and
passv are exactly the same. for some reason, it doen't go in to the if
statement Any syggestions?

Use std::string instead of char*.

Btw. the if statement doesn't check for all possible outcomes, and
it's very unclear who's got deallocation responsibility for pass and
passv.

Both these problems are solved by using std::string.

 

[Robert Bauck Hamar]

I have a problem with the int strcmp(str1,str2) function:

When I do:

char *pass;
char *passv;

pass = getpass("Please enter.....");
passv = getpass("Please verify.....");

if(strcmp(pass,passv)==1) // i.e. failure{
cout<<"Verification failed!<<endl;
exit(1);
}

Problem: Does't seem to work properly, even though the strings, pass and
passv are exactly the same. for some reason, it doen't go in to the if
statement Any syggestions?

strcmp returns 0 if the two strings are equal. It returns a value less
than 0 if the first string is "less than" the second or a value greater
than 0 if the first string is "greater than" the second. I've never
seen anyone stating it should return the value 1 in any circumstance.
You might use:

#include <string>
#include <iostream>
#include <unistd.h> //[0]

//...
std::string pass = getpass("Please enter...");
std::string passv = getpass("Please verify...");

if (pass != passv) {
std::cout << "Doesn't match.\n";
exit(1);
}

// End code
[0]: According to my documentation, char *getpass(const char*) is
declared in the nonstandard header unistd.h. It returns a pointer to
static memory, which might get overwritten by any sequential call to
getpass. This could make sure the two strings always compare equal in
mr. Jones' code. The use of std::string would fix this.

 

[Siemel Naran]

I have a problem with the int strcmp(str1,str2) function:

When I do:

char *pass;
char *passv;

pass = getpass("Please enter.....");
passv = getpass("Please verify.....");

if(strcmp(pass,passv)==1) // i.e. failure{
cout<<"Verification failed!<<endl;
exit(1);
}

As others have pointed out, strcmp returns negative, zero, or positive. You
can't attach significance to the particular positive or negative number
returned, as the number varies by implementation. To test if two strings
are not equal, just check if strcmp is not equal to zero.

But there's another issue.

Does getpass return a pointer to a static char[] array? If so, then you
don't have to delete the array, but each successive call to getpass will
overwrite the previous value in the char[] array, so by definition
strcmp(pass, passv) will always be zero. To check if this is so, perform
cout << (pass == passv); to compare the values of the pointers. Use
std::string to copy the char[] array into a string, then feel free to call
getpass again, as in Rolf's and Robert's code. As a bonus, you get to use
!=, which is easier to read than strcmp(...)==0.

 

[JKop]

BrianJones posted:

I have a problem with the int strcmp(str1,str2) function:

When I do:

char *pass;
char *passv;

pass = getpass("Please enter.....");
passv = getpass("Please verify.....");

if(strcmp(pass,passv)==1) // i.e. failure{
cout<<"Verification failed!<<endl;
exit(1);
}

Problem: Does't seem to work properly, even though the strings, pass and
passv are exactly the same. for some reason, it doen't go in to the if
statement Any syggestions?

Cheers,
Ben

Without a definition of "getpass", I can only guess at...

Do you think there's anything wrong with the following:

int main()
{
int* jk;

*jk = 4;
}


-JKop

 

[Default User]

But there's another issue.

Does getpass return a pointer to a static char[] array? If so, then you
don't have to delete the array, but each successive call to getpass will
overwrite the previous value in the char[] array, so by definition
strcmp(pass, passv) will always be zero.

It certainly is that way on my Solaris implementation:


USAGE
The return value points to static data whose content may be
overwritten by each call.


I'm not sure, but I think getpass() is POSIX and likely has the same
behavior on other implementations. The newsgroup comp.unix.programmer
would be a good place to discuss that if the OP needs further
information.



Brian Rodenborn