R – How to extract a single function from a source file

c++code-metricsmccregextext-processing

I'm working on a small academic research about extremely long and complicated functions in the Linux kernel. I'm trying to figure out if there is a good reason to write 600 or 800 lines-long functions.

For that purpose, I would like to find a tool that can extract a function from a .c file, so I can run some automated tests on the function.

For example, If I have the function cifs_parse_mount_options() within the file connect.c, I'm seeking a solution that would roughly work like:

extract /fs/cifs/connect.c cifs_parse_mount_options

and return the 523 lines of code(!) of the function, from the opening braces to the closing braces.

Of course, any way of manipulating existing software packages like gcc to do that, would be most helpful too.

Thanks,

Udi

EDIT : The answers to Regex to pull out C function prototype declarations? convinced me that matching function declaration by regex is far from trivial.

Best Solution

Why don't you write a small PERL/PHP/Python script or even a small C++,Java or C# program that does that?

I don't know of any already-made tools to do that but writing the code to parse out the text file and extract a function body from a C++ code file should not take more than 20 lines of code.. The only difficult part will be locating the beginning of the function and that should be a relatively simple task using RegEx. After that, all you need is to iterate through the rest of the file keeping track of opening and closing curly braces and when you reach the function body closing brace you're done.

Setting a bit

Use the bitwise OR operator (|) to set a bit.

number |= 1UL << n;

That will set the nth bit of number. n should be zero, if you want to set the 1st bit and so on upto n-1, if you want to set the nth bit.

Use 1ULL if number is wider than unsigned long; promotion of 1UL << n doesn't happen until after evaluating 1UL << n where it's undefined behaviour to shift by more than the width of a long. The same applies to all the rest of the examples.

Clearing a bit

Use the bitwise AND operator (&) to clear a bit.

number &= ~(1UL << n);

That will clear the nth bit of number. You must invert the bit string with the bitwise NOT operator (~), then AND it.

Toggling a bit

The XOR operator (^) can be used to toggle a bit.

number ^= 1UL << n;

That will toggle the nth bit of number.

Checking a bit

You didn't ask for this, but I might as well add it.

To check a bit, shift the number n to the right, then bitwise AND it:

bit = (number >> n) & 1U;

That will put the value of the nth bit of number into the variable bit.

Changing the nth bit to x

Setting the nth bit to either 1 or 0 can be achieved with the following on a 2's complement C++ implementation:

number ^= (-x ^ number) & (1UL << n);

Bit n will be set if x is 1, and cleared if x is 0. If x has some other value, you get garbage. x = !!x will booleanize it to 0 or 1.

To make this independent of 2's complement negation behaviour (where -1 has all bits set, unlike on a 1's complement or sign/magnitude C++ implementation), use unsigned negation.

number ^= (-(unsigned long)x ^ number) & (1UL << n);

unsigned long newbit = !!x;    // Also booleanize to force 0 or 1
number ^= (-newbit ^ number) & (1UL << n);

It's generally a good idea to use unsigned types for portable bit manipulation.

number = (number & ~(1UL << n)) | (x << n);

(number & ~(1UL << n)) will clear the nth bit and (x << n) will set the nth bit to x.

It's also generally a good idea to not to copy/paste code in general and so many people use preprocessor macros (like the community wiki answer further down) or some sort of encapsulation.

Unix – How to extract a predetermined range of lines from a text file on Unix

sed -n '16224,16482p;16483q' filename > newfile

From the sed manual:

p - Print out the pattern space (to the standard output). This command is usually only used in conjunction with the -n command-line option.

n - If auto-print is not disabled, print the pattern space, then, regardless, replace the pattern space with the next line of input. If there is no more input then sed exits without processing any more commands.

q - Exit sed without processing any more commands or input. Note that the current pattern space is printed if auto-print is not disabled with the -n option.

and

Addresses in a sed script can be in any of the following forms:

number Specifying a line number will match only that line in the input.

An address range can be specified by specifying two addresses separated by a comma (,). An address range matches lines starting from where the first address matches, and continues until the second address matches (inclusively).