Re: [libmicrohttpd] Run-Time Check Failure(Static Link in Debug)

[Evgeny Grin]

VS run-time warnings are nice.
However, they warn even when explicit casting is used, which is not 
nice. Explicit cast means that data truncation is intentional.

The suggested "fix" would not change the resulting binary *if compiler 
is smart enough*. MHD is very portable and can be built by many various 
compiler.
I don't think that changing the code just to satisfy a single compiler 
is good idea if such change could potentially influence resulting 
binaries on other compilers. Code readability could be hurt as well.

VS project have been corrected to completely disable these warnings.
Also I've added compiler pragmas to explicitly disable such checks in 
some specific functions, so it is still possible to enable run-time 
checks in project settings and use MHD. However, I'm not sure that 
individual explicit disable pragmas cover all functions, where such 
checks must be disabled.

--
Evgeny

On 13.09.2023 10:58, luozhaotian wrote:
> Visual Studio show this Debug Error:
>
> Run-Time Check Failure #1 - A cast to a smaller data type has caused a 
> loss of data.  If this was intentional, you should mask the source of 
> the cast with the appropriate bitmask.  For example:
>
>         char c = (i & 0xFF);
>
> Changing the code in this way will not affect the quality of the 
> resulting optimized code.
>
> After debug, I find the reason is cast to uint8_t.  When cast values 
> bigger than 256 to uint8_t in line 1421-1423,  the Debug Error will be 
> triggered.
>
> //mhd_str.c
>
> size_t
>
> MHD_base64_to_bin_n (const char *base64,
>
>                       size_t base64_len,
>
>                       void *bin,
>
>                       size_t bin_size){
>
>       //……
>
> 1421      out[j + 0] = (uint8_t) ((((uint8_t) v1) << 2) | (((uint8_t) 
> v2) >> 4));
>
> 1422      out[j + 1] = (uint8_t) ((((uint8_t) v2) << 4) | (((uint8_t) 
> v3) >> 2));
>
> 1423      out[j + 2] = (uint8_t) ((((uint8_t) v3) << 6) | (((uint8_t) v4)));
>
>     //……
>
> }
>
> In Visual Studio, the Debug mode default open /RTC1, but the Release 
> mode doesn’t.
>
> As the suggestion by Visual Studio, if we modify the current git 
> master(mhd_str.c) to:
> 2375      out[j + 0] = (uint8_t) ((((uint8_t) ((((uint8_t) v1) << 2)&0xFF))
>                                | ((uint8_t) (((uint8_t) v2) >> 4))) & 0xFF);
> 2377      out[j + 1] = (uint8_t) ((((uint8_t) ((((uint8_t) v2) << 4) & 
> 0xFF))
>                                | ((uint8_t) (((uint8_t) v3) >> 2))) & 0xFF);
> 2379      out[j + 2] = (uint8_t) ((((uint8_t) ((((uint8_t) v3) << 6)&0xFF))
>                                | ((uint8_t) (((uint8_t) v4)))) & 0xFF);
>
> The error didn'tn  appear.
>
> Otherwise, if we ignore the error, the program still works.

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