"Error: comparison between pointer and integer" when compiling c++ code

Question

In C++ (compiler : clang++), when compiling the following code:

char* strcpy(char * dest, const char * src)
{
    char* result = dest;
    if(('\0' != dest) && ('\0' != src))
    {
        /* Start copy src to dest */
        while ('\0' != *src)
        {
            *dest++ = *src++;
        }
        /* put '\0' termination */
        *dest = '\0';
    }
    return result;

}

I get the following error code:

string/strcpy.cpp:12:11: error: comparison between pointer and integer
      ('int' and 'char *')
        if(('\0' != dest) && ('\0' != src))
            ~~~~ ^  ~~~~
string/strcpy.cpp:12:29: error: comparison between pointer and integer ('int'
      and 'const char *')
        if(('\0' != dest) && ('\0' != src))

I'm aware that most of the errors related with this error are produced when the characters to compare are between quotation marks instead of apostrophes, but in this code this is not the case. Why is this error produced? Thanks in advance!

dest is a pointer. *dest is the value of the thing it points to. You compare correctly later with '\0' != *src. Seems like a simple typo to me. — François Andrieux
– François Andrieux, Commented Jan 12, 2018 at 19:01
@manni66 In the freestanding environment that I'm using strcpy is a valid name — Rottenheimer2
– Rottenheimer2, Commented Jan 12, 2018 at 19:05

pm100 · Accepted Answer · 2018-01-12 21:21:03Z

1

you mean

if((NULL != dest) && (NULL != src))

of even more idiomatic

if((dest) && (src))

edited Jan 12, 2018 at 21:21

answered Jan 12, 2018 at 19:11

pm100

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Comments

Qwertycrackers · Accepted Answer · 2018-01-12 19:14:45Z

1

('\0' != dest)

In the above, '\0' is a char literal, but dest is a pointer to a char. This is the reason for the error being thrown.

I believe the problem would be fixed if you change the conditional to

('\0' != *dest)

EDIT: Whoops, I thought you were trying to check if the string is at it's end. If you were trying to check if the pointer is null, the correct way would be to simply evaluate it as conditional.

if(dest)

edited Jan 12, 2018 at 19:14

answered Jan 12, 2018 at 19:03

Qwertycrackers

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1 Comment

John Bollinger Over a year ago

Oddly enough, although the correction you propose would indeed resolve the type mismatch, I don't think it's the right correction for the context. It doesn't make sense. I think the OP means to perform null-pointer checks there.

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