Question

memcpy pointer type conversion from 'void *' to 'tm *'

Asked by: ispaleny

Hi,

I want to use some old C library code in my Visual Studio project. All works like a charm, except this code:

static struct tm *localtime_r(const time_t *tloc, struct tm *result) {
      struct tm *tm;
      if((tm = localtime(tloc)))
            return memcpy(result, tm, sizeof(struct tm));
      return 0;
}

Compilation aborts with:

    SomeCode.c(106): error C2440: '=' : cannot convert from 'void *' to 'tm *'

I tried:

   return (tm *) memcpy(result, tm, sizeof(struct tm));

with no luck.

Will you help me?

Thanks,

Ivo



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Asked On
2006-08-01 at 07:49:11ID21939152
Tags

memcpy

,

pointer

,

convert

Topic

Miscellaneous Programming

Participating Experts
1
Points
250
Comments
5

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Answers

 

by: StillUnAwarePosted on 2006-08-01 at 07:58:46ID: 17224418

this should be:

static struct tm *localtime_r(const time_t *tloc, struct tm *result) {
     struct tm *tmvar;
     if((tmvar == (tm*)localtime(tloc)))
          return (tm*)memcpy(result, tmvar, sizeof(struct tm));
     return 0;
}

 

by: ispalenyPosted on 2006-08-01 at 08:21:52ID: 17224685

Works nice.

But I don't think "if (tmvar = localtime(tloc))" was a mistyped "if (tmvar == localtime(tloc))". I would have nothing to return from the function.

Andrius, thank you very much.

 

by: StillUnAwarePosted on 2006-08-01 at 08:26:30ID: 17224732

Well I am already forgetting C, I'm deep in Java now, so I thought the comparison should be "==" and not "=", but if that works, then I must have loosing my power :)

 

by: ispalenyPosted on 2006-08-01 at 08:34:43ID: 17224813

It is a classic C, something like

if (a=fn()) {...}

1. Variable a is filled by fn() result
2. If result is not zero, condition is true and run ...

I also don't like such a "fast" coding.

 

by: StillUnAwarePosted on 2006-08-01 at 08:37:39ID: 17224837

oh, yeah, now I got it, it wasn't comparison, it was assignment and check whether the value equals to NULL. Then everything is right.

20120131-EE-VQP-002

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