JsonVariant::operator|

Description

Changes the value returned when the JsonVariant is undefined or incompatible.

In other words, it changes the default value.

This feature was introduced in version 5.12.

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 is the JsonVariant is undefined or incompatible.

Return value

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

Remark: even if JsonVariant::is<char*>() returns true for null, the operator | returns defaultValue when that happens.

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;