Coding guide

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Coding Guide



Code Format

We want to try and make a consistent look and feel to the code in GNU Radio. Here are a few things to try to keep in mind while writing code.

All lines of code should not exceed 70 characters on a width. Often, there is a logical break in the line of code that allows it to easily span two lines, such as between arguments to the function. Sometimes not, though, so make your best judgement here. The reason for this is to make the code format easily readable in both an editor and when printed out.

As stated elsewhere, no CamelCase. All distinct words in a function or variable name should use underscores:

int foo_bar

In the header file, functions should all be written on the same line, up to the 70-character limit.

int bar(int arg1, int arg2);

In the C++ implementation file, the function should have its return data type indicated on a separate line.

int foo::bar(int arg1, int arg2)

Curly brace convention is as follows. After a function name, the curly brace should follow on the next line, and the ending curly brace should be on its own line. Inside of a function, such as for an if statement or for loop, the beginning curly brace should come after the statement, while the end curly brace should be on its own line.

int foo::bar(int arg1, int arg2)
if(arg1 == 0) {
   do something;
} else {
   do something else;
return 0;

Although C++ allows single-line statements after a for or if statement to exist without curly braces surrounding them, it is recommended to always use curly braces. This may help prevent problems in the future if another line is added to the code block.

Unit testing

Build unit tests for everything non-trivial and run them after every change. Check out Extreme Programming:

Unit tests should also be written for all examples. This should kill off the bit rot we've been plagued with.

Unit tests can be written in Python or in C++. If possible, use Python unit tests (e.g. to test the output of signal processing blocks).

Standard command line options

When writing programs that are executable from the command line, please follow these guidelines for command line argument names (short and long) and types of the arguments. We list them below using the Python optparse syntax. In general, the default value should be coded into the help string using the "... [default=%default]" syntax.

USRP source

Any program using a USRP source (usrp.source_*) shall include:

add_option("", "--which-usrp", type="intx", default=0,
help="select which USRP to use [default=%default]")
add_option("-R", "--rx-subdev-spec", type="subdev", default=(0, 0),
help="select USRP Rx side A or B [default=A]")
You are free to change the default if it makes sense in your application.

=== USRP sink ===

Any program using a USRP sink (usrp.sink_*) shall include:
<syntaxhighlight lang="c++">
add_option("", "--which-usrp", type="intx", default=0,
help="select which USRP to use [default=%default]")
add_option("-T", "--tx-subdev-spec", type="subdev", default=(0, 0),
help="select USRP Tx side A or B [default=A]")

You are free to change the default if it makes sense in your application.

Audio source

Any program using an audio source shall include:

add_option("-I", "--audio-input", type="string", default="",
help="pcm input device name. E.g., hw:0,0 or /dev/dsp")

The default must be "". This allows an audio module-dependent default
to be specified in the user preferences file.

Audio sink

add_option("-O", "--audio-output", type="string", default="",
help="pcm output device name. E.g., hw:0,0 or /dev/dsp")

The default must be "". This allows an audio module-dependent default
to be specified in the user preferences file.

Standard options names by parameter

Whenever you want an integer, use the "intx" type. This allows the
user to input decimal, hex or octal numbers. E.g., 10, 012, 0xa.

Whenever you want a float, use the "eng_float" type. This allows the
user to input numbers with SI suffixes. E.g, 10000, 10k, 10M, 10m, 92.1M

If your program allows the user to specify values for any of the
following parameters, please use these options to specify them:

To specify a frequency (typically an RF center frequency) use:

add_option("-f", "--freq", type="eng_float", default=<your-default-here>,
help="set frequency to FREQ [default=%default]")

To specify a decimation factor use:

add_option("-d", "--decim", type="intx", default=<your-default-here>,
help="set decimation rate to DECIM [default=%default]")

To specify an interpolation factor use:

add_option("-i", "--interp", type="intx", default=<your-default-here>,
help="set interpolation rate to INTERP [default=%default]")

To specify a gain setting use:

add_option("-g", "--gain", type="eng_float", default=<your-default-here>,
help="set gain in dB [default=%default]")

If your application specifies both a tx and an rx gain, use:

add_option("", "--rx-gain", type="eng_float", default=<your-default-here>,
help="set receive gain in dB [default=%default]")
add_option("", "--tx-gain", type="eng_float", default=<your-default-here>,
help="set transmit gain in dB [default=%default]")

To specify the number of channels of something use:

add_option("-n", "--nchannels", type="intx", default=1,
help="specify number of channels [default=%default]")

To specify an output filename use:

add_option("-o", "--output-filename", type="string", default=<your-default-here>,
help="specify output-filename [default=%default]")

To specify a rate use:

add_option("-r", "--bit-rate", type="eng_float", default=<your-default-here>,
help="specify bit-rate [default=%default]")


add_option("-r", "--sample-rate", type="eng_float", default=<your-default-here>,
help="specify sample-rate [default=%default]")

If your application has a verbose option, use:

add_option('-v', '--verbose', action="store_true", default=False,
help="verbose output")

If your application allows the user to specify the "fast USB" options, use:

add_option("", "--fusb-block-size", type="intx", default=0,
help="specify fast usb block size [default=%default]")
add_option("", "--fusb-nblocks", type="intx", default=0,
help="specify number of fast usb blocks [default=%default]")


Global names

All globally visible names (types, functions, variables, consts, etc) shall begin with a "package prefix", followed by an '_'. The bulk of the code in GNU Radio logically belongs to the "gr" package, hence names look like gr_open_file (...).

Large coherent bodies of code may use other package prefixes, but let's try to keep them to a well thought out list. See the list below.

Package prefixes

These are the current package prefixes:

gr_: Almost everything

gri_: Implementation primitives. Sometimes we have both a gr_<foo> and a gri_<foo>. In that case, gr_<foo> would be derived from gr_block and gri_<foo> would be the low level guts of the function.

usrp_: Universal Software Radio Peripheral

qa_: Quality Assurance. Test code.

atsc_: Code related to the Advanced Television Standards Committee HDTV implementation

Naming conventions

  • Functions and variable names should be underscore_separated_words (No CamelCase).
  • All data members of a class should be made clear by using a "d_" prefix to them. They should also be private unless there is a very good reason not to.

All data member should have a settable and gettable accessor function of the form:

  • void set_variable(type var);
  • type variable();

These accessors should perform any required range checking and throw a "std::out_of_range" exceptions when not met. Other conditions that are not met can throw a "std::invalid_argument" exception.

  • All class data members shall begin with d_<foo>.

The big win is when you're staring at a block of code it's obvious which of the things being assigned to persist outside of the block. This also keeps you from having to be creative with parameter names for methods and constructors. You just use the same name as the instance variable, without the d_.


class gr_wonderfulness {
  std::string   d_name;
  double    d_wonderfulness_factor;

  gr_wonderfulness (std::string name, double wonderfulness_factor)
    : d_name (name), d_wonderfulness_factor (wonderfulness_factor)

' All class static data members shall begin with s_<foo>.

Accessor Functions

All signal processing blocks should have accessors to get and set values. For parameter param, the get function is param() and the set function is set_param(type new_value) for any variables that can be changed at runtime.

File names

Each significant class shall be contained in it's own file. The declaration of class gr_foo shall be in gr_foo.h, the definition in

Storage management

Strongly consider using the boost smart pointer templates, scoped_ptr and shared_ptr. scoped_ptr should be used for locals that contain pointers to objects that we need to delete when we exit the current scope. shared_ptr implements transparent reference counting and is a major win. You never have to worry about calling delete. The right thing happens.



Use the following exceptions:

  • std::runtime_error: when a runtime error has occurred
  • std::out_of_range: when a variable to be set is not within a given range
  • std::invalid_argument: when an argument is set to an improper value

C++ unit tests

For C++ we're using the cppunit framework. cppunit has its bad smells, but it's mostly workable.

Currently each directory <dirname> contains files qa_<dirname>.{h,cc} that bring together all the qa_<foo> test suites in the directory. We ought to be able to automate this without too much trouble.

The directory gnuradio-core/src/tests contains programs that run the tests. test_all runs all of the registered C++ unit tests.

As far as I can tell, the cppunit TestFactoryRegistry maybe able to be tricked into doing what we want. As is, I don't think it's enough by itself, since there's nothing dragging the qa* files out of the library and into the program. I haven't tested out this idea.


Python unit tests

We use the standard unittest package for unit testing of Python code.

Block naming conventions

Blocks should be given a name that indicates its purpose as well as its input and output data types. If a block lives in the GNU Radio core and performs the function FOO that takes complex in and produces floating points outputs, it's name should be:


This boils down to:


The module is the name of the GNU Radio namespace the block belongs to. Most blocks live inside, but some, like the new digital modulation information, live elsewhere. The digital blocks, for instance, are in These blocks are appropriately named digital_foo_cf.

The name indicates the function of the block, such as "add" or "fir_filter".

The input indicates the input type while output indicates the output type. Currently, the types are:

  • c: complex (32-bit floats for both I and Q)
  • f: float (32-bit single precision IEEE 754 style)
  • i: integer (32-bit signed integers)
  • s: short (16-bit signed integers)
  • b: bytes (8-bit signed integers)

There is no differentiation between bytes and bits, even though some blocks use unpacked format where a single bit is represented in a byte. If this is the case, it should be made clear in the documentation for the block.

GNU Radio also has a concept of vectors, where the data into or out of the block are vectors of items. The "v" is then used to indicate if this is the case. A block that uses vectors should indicate it by the type:

<vector in><input><vector out><output>

So a block that takes vectors in but streams samples out would look like vcc, but a block that does vectors for both input and output will look like vcvc.

NOTE: this is a new convention and older blocks that use vectors do not follow this. They generally only indicate that vectors are used somewhere by putting a single "v" in front of the data type indicator.