# Extra Clang Tools 22.1.2 documentation

## clang-tidy - misc-throw-by-value-catch-by-reference

# misc-throw-by-value-catch-by-reference

cert-err09-cpp and cert-err61-cpp redirect here as aliases of this check.

Finds violations of the rule “Throw by value, catch by reference” presented for example in “C++ Coding Standards” by H. Sutter and A. Alexandrescu, as well as the CERT C++ Coding Standard rule ERR61-CPP. Catch exceptions by lvalue reference.

Exceptions:

  - Throwing string literals will not be flagged despite being a pointer. They are not susceptible to slicing and the usage of string literals is idiomatic.

  - Catching character pointers (`char`, `wchar_t`, unicode character types) will not be flagged to allow catching string literals.

  - Moved named values will not be flagged as not throwing an anonymous temporary. In this case we can be sure that the user knows that the object can’t be accessed outside catch blocks handling the error.

  - Throwing function parameters will not be flagged as not throwing an anonymous temporary. This allows helper functions for throwing.

  - Re-throwing caught exception variables will not be flagged as not throwing an anonymous temporary. Although this can usually be done by just writing `throw;` it happens often enough in real code.

## Options

CheckThrowTemporaries

  Triggers detection of violations of the CERT recommendation ERR09-CPP. Throw anonymous temporaries. Default is true.

WarnOnLargeObject

  Also warns for any large, trivial object caught by value. Catching a large object by value is not dangerous but affects the performance negatively. The maximum size of an object allowed to be caught without warning can be set using the MaxSize option. Default is false.

MaxSize

  Determines the maximum size of an object allowed to be caught without warning. Only applicable if `WarnOnLargeObject` is set to true. If the option is set by the user to std::numeric_limits<uint64_t>::max() then it reverts to the default value. Default is the size of size_t.