CODEWITHSUNDEEP
c++strcmp
Joe
Joe

Reputation: 79

2 Failed test with my strcmp function

The code below is in my header file:

int mystrcmp(const char *s1, const char *s2) // strcmp function
{
    while(*s1 == *s2)
    {
        if(*s1 == '\0' || *s2 == '\0')
            break;

        s1++;
        s2++;
    }

    if(*s1 == '\0' && *s2 == '\0')
        return (0);
    else
        return (-1);
}

The problem is when I run it my main.cpp says it fails 2 test

Below is an excerpt from my main.cpp:

void testmystrcmp(void)
{
   int iResult;

   iResult = mystrcmp("Ruth", "Ruth");
   ASSURE(iResult == 0);

   iResult = mystrcmp("Gehrig", "Ruth");
   ASSURE(iResult < 0);

   iResult = mystrcmp("Ruth", "Gehrig");
   ASSURE(iResult > 0);  // right here mystrcmp fails the test

   iResult = mystrcmp("", "Ruth");
   ASSURE(iResult < 0);

   iResult = mystrcmp("Ruth", "");
   ASSURE(iResult > 0);

   iResult = mystrcmp("", "");
   ASSURE(iResult == 0); // it also fails the test here but why??
}

Note: I cannot change the .cpp file

I have been trying to fix this issue but do not know how.

Upvotes: 0

Views: 736

Answers (5)

user2548608
user2548608

Reputation:

Hmmm... your mystrcmp function does not fail the second test.

http://ideone.com/ZcW02n

#include <iostream>

int mystrcmp(const char *s1, const char *s2) // strcmp function
{
    while(*s1 == *s2)
    {
        if(*s1 == '\0' || *s2 == '\0')
            break;

        s1++;
        s2++;
    }

    if(*s1 == '\0' && *s2 == '\0')
        return (0);
    else
        return (-1);
}

int main() {
        std::cout << mystrcmp("","") << std::endl;
        return 0;
}

 output: 0

Upvotes: 0

SigTerm
SigTerm

Reputation: 26439

As other people said, strcmp is supposed to return positive and negative numbers.

Try this instead:

int mystrcmp(const char *s1, const char *s2){
    for(;*s1 && *s2 && (*s1 == *s2); s1++, s2++){}
    return *s1 - *s2;
}

Upvotes: 0

Mats Petersson
Mats Petersson

Reputation: 129524

strcmp is defined to return a positive value if the "first" string is greater than the "second" string, a zero value if they are equal and a negative value if the "first" is less than the "second" string. So if the strings are not equal, you should decide which one is greater and then return the appropriate value.

An easy way to achieve that is to return *s1 - *s2 (which also returns 0 when they are equal, as a bonus).

Upvotes: 5

Jashaszun
Jashaszun

Reputation: 9270

Well, in your mystrcmp function, I see no spot where you return a positive number, so the compare between "Ruth" and "Gehrig" will always fail.

Upvotes: 2

Unsigned
Unsigned

Reputation: 9936

You only ever return -1 or 0. Read the assertions, why are they failing?

Also, on line 5, you only need to check either *s1=='\0' or *s2=='\0', since you know they're equal due to the while condition.

Upvotes: 0

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