JsonVariant::operator|

Description

JsonVariant::operator|() provides default value for a JsonVariant.

Signatures

bool operator|(bool defaultValue) const; float operator|(float defaultValue) const; double operator|(double defaultValue) const; signed char operator|(signed char defaultValue) const; unsigned char operator|(unsigned char defaultValue) const; signed int operator|(signed int defaultValue) const; unsigned int operator|(unsigned int defaultValue) const; signed short operator|(signed short defaultValue) const; unsigned short operator|(unsigned short defaultValue) const; signed long operator|(signed long defaultValue) const; unsigned long operator|(unsigned long defaultValue) const; unsigned long long operator|(unsigned long long defaultValue) const; // <- may require ARDUINOJSON_USE_LONG_LONG signed long long operator|(signed long long defaultValue) const; // <- may require ARDUINOJSON_USE_LONG_LONG const char* operator|(char* defaultValue) const; const char* operator|(const char* defaultValue) const; String operator|(String defaultValue) const; std::string operator|(const std::string& defaultValue) const; 

Arguments

defaultValue: the value to return if the JsonVariant is null or incompatible with the requested type.

Unlike JsonVariant::as<T>() that uses a template parameter to specify the requested type, JsonVariant::operator|() infers the requested type from the argument defaultValue. Usually, that’s what you want but can lead to odd results as described below.

Return value

The value of the variant, if it can be converted to the type of defaultValue.
defaultValue if not.

Example

int port = config["port"] | 80; strlcpy(hostname, config["hostname"] | "example.com", sizeof(hostname)); 

Pitfall ⚠️

When you use this operator, the type of the expression is inferred from the type of the default value.

Here is an example where this fact matters:

long value = root["key"] | -1; 

In this example, the right side of the expression returns an int (and not a long as one could expect) because the default value is an integer. If root["key"] contains a big value, the integer overflows, and you get a seemingly random result in value.

To fix this, you need to change the type of the default value:

long value = root["key"] | -1L; 

Lastly, you cannot combine this operator with JsonVariant::as<T>(). For example, you cannot write:

// this line compiles but it doesn't do what you think long value = root["key"].as<long>() | 1; // WRONG!!!! 