C++ OR used on strings

Richard Langner

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Jan 19, 2022, 9:20:11 AM1/19/22

to Sheffield Hardware Hackers

On this page there is an OR operator which is a single pipe character (|)

  // Copy values from the JsonDocument to the Config
  config.port = doc["port"] | 2731;
  strlcpy(config.hostname,                  // <- destination
          doc["hostname"] | "example.com",  // <- source
          sizeof(config.hostname));         // <- destination's capacity

If the first parameter can't be found it returns the second on these lines

config.port = doc["port"] | 2731;

and

doc["hostname"] | "example.com"

I've not seen this before and wonder why it's not doing a bitwise OR as I would expect from the single pipe (|) character.

Can anyone point me to guidance on this?

Richard

nop head

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Jan 19, 2022, 10:53:42 AM1/19/22

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The port is an int, not a string, so it should definitely do a bitwise OR, which is a bug as far as I can see. Perhaps they should be both ||.

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Richard Langner

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Jan 19, 2022, 10:57:15 AM1/19/22

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As I understand it, single pipe is bitwise OR, double pipe is logical OR.

On 19/01/2022 15:53, nop head wrote:

The port is an int, not a string, so it should definitely do a bitwise OR, which is a bug as far as I can see. Perhaps they should be both ||.

On Wed, 19 Jan 2022 at 14:20, Richard Langner <richard...@gmail.com> wrote:
On this page there is an OR operator which is a single pipe character (|)
  // Copy values from the JsonDocument to the Config
  config.port = doc["port"] | 2731;
  strlcpy(config.hostname,                  // <- destination
          doc["hostname"] | "example.com",  // <- source
          sizeof(config.hostname));         // <- destination's capacity
If the first parameter can't be found it returns the second on these lines
config.port = doc["port"] | 2731;
and
doc["hostname"] | "example.com"
I've not seen this before and wonder why it's not doing a bitwise OR as I would expect from the single pipe (|) character.

Can anyone point me to guidance on this?

Richard
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Graham Driver

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Jan 19, 2022, 11:37:03 AM1/19/22

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Google says that | can be used as a non-short-circuiting version of ||. I understand the concept but have no idea about the implications.

In any event I guess the chap is looking for something being false, null, empty or zero.

From: sheffield-har...@googlegroups.com <sheffield-har...@googlegroups.com> on behalf of Richard Langner <richard...@gmail.com>
Sent: 19 January 2022 15:57
To: sheffield-har...@googlegroups.com <sheffield-har...@googlegroups.com>
Subject: Re: [SHH:17341] C++ OR used on strings

To view this discussion on the web, visit https://groups.google.com/d/msgid/sheffield-hardware-hackers/4dd3c272-5212-9bd7-1409-9a149c60b06f%40gmail.com.

Paul M

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Jan 19, 2022, 5:22:36 PM1/19/22

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Hi Richard,

I guess you didn't spot this bit on that page:

JsonVariant
JsonVariant::operator|

Links to https://arduinojson.org/v6/api/jsonvariant/or/

It's using operator overloading on that class to change what a normal "|" (bitwise or) would usually do.

Regards,
Paul

On Wed, 19 Jan 2022 16:37:01 +0000
Graham Driver <graham...@hotmail.com> wrote:

> Google says that | can be used as a non-short-circuiting version of ||. I understand the concept but have no idea about the implications.
>
> In any event I guess the chap is looking for something being false, null, empty or zero.
>
> ________________________________
> From: sheffield-har...@googlegroups.com <sheffield-har...@googlegroups.com> on behalf of Richard Langner <richard...@gmail.com>
> Sent: 19 January 2022 15:57
> To: sheffield-har...@googlegroups.com <sheffield-har...@googlegroups.com>
> Subject: Re: [SHH:17341] C++ OR used on strings
>
> As I understand it, single pipe is bitwise OR, double pipe is logical OR.
> ________________________________
>
> On 19/01/2022 15:53, nop head wrote:
> The port is an int, not a string, so it should definitely do a bitwise OR, which is a bug as far as I can see. Perhaps they should be both ||.
>
> ________________________________

> On Wed, 19 Jan 2022 at 14:20, Richard Langner <richard...@gmail.com<mailto:richard...@gmail.com>> wrote:
> On this page<https://arduinojson.org/v6/example/config/> there is an OR operator which is a single pipe character (|)

>
>
> // Copy values from the JsonDocument to the Config
> config.port = doc["port"] | 2731;
> strlcpy(config.hostname, // <- destination

> doc["hostname"] | "example.com<http://example.com>", // <- source

> sizeof(config.hostname)); // <- destination's capacity
>
>
> If the first parameter can't be found it returns the second on these lines
>
> config.port = doc["port"] | 2731;
>
> and
>

> doc["hostname"] | "example.com<http://example.com>"

>
>
> I've not seen this before and wonder why it's not doing a bitwise OR as I would expect from the single pipe (|) character.
>
> Can anyone point me to guidance on this?
>
> Richard
>
>
>
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>
>
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Richard Langner

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Jan 20, 2022, 12:46:21 PM1/20/22

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Thanks Paul, I had not seen it at the bottom of the page.
I decided to try out the code in VSC but the compiler won't let me put an incompatible type or NULL as the first argument, so the code will never get to the default value.

Richard

On 19/01/2022 22:22, Paul M wrote:

Hi Richard,

I guess you didn't spot this bit on that page:

JsonVariant
    JsonVariant::operator|

Links to https://arduinojson.org/v6/api/jsonvariant/or/

It's using operator overloading on that class to change what a normal "|" (bitwise or) would usually do.

Regards,
Paul

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