View on GitHub

Flight Software & Embedded Systems Framework

Asserts in F

The F′ framework uses asserts to perform run-time checks for software errors. They are a method for verifying conditions that should be true unless there is a software or processor error. Assert.hpp defines macros to declare an assertion in C++ code. CAssert.hpp defines macros to declare an assertion in C code.

The definition for the framework assert is found in Fw/Types/Assert.hpp. The user calls the FW_ASSERT(cond, arg1, ...) macro with up to six arguments. The arguments can consist of any basic types shown below.

  • I8 8-bit signed integer

  • U8 8-bit unsigned integer

  • I16 16-bit signed integer

  • U16 16-bit unsigned integer

  • I32 32-bit signed integer

  • U32 32-bit unsigned integer

  • F32 32-bit IEEE floating point number (float)

  • F64 64-bit floating point number (double)

  • I64 64-bit signed integer

  • U64 64-bit unsigned integer

  • bool C++ Boolean type

These types are used in XML specifications. Note that not all types are available on all processor architectures. The types that are available is a configurable feature of the architecture and is typically set by compiler arguments.

The assert can be configured in the following ways:

  • FW_ASSERT_LEVEL Sets the level or reporting for the asserts.

    • FW_NO_ASSERT Shows the asserts turned off. The code to check the condition is not compiled. Some developers prefer this once the code has been tested to regain some processing performance.

    • FW_FILEID_ASSERT Identifies an integer value for the file where the assert occurs (as opposed to __FILE__). It saves code space since no file name is stored.

    • FW_FILENAME_ASSERT Identifies which file the assert occurred in. (The __FILE__ macro is used.)

  • FW_ASSERT_TEXT_SIZE Identifies the size of the buffer used to store the text of the assert.


By default, when FW_ASSERT is called the framework prints a message (location of and arguments to the macro), and then calls the C assert() function. The framework also provides a function that allows the registration of a user-defined handler. The handler is registerAssertHook and can be found in FwAssert.hpp. The assert hook is called with a string representing the text of the assert. The user implements a derived class that implements the reportAssert() pure virtual method, and does whatever project specific logic is required.


When formatting an assert message use the default message line hash or name, and argument approach.


When outputting the assert message use the default Fw::Logger. Force the Fw::Logger default to printf for systems with print f.


Actually asserts (action of assert).