c++ macro for saving enum element names and values to file - c++

Question

Normally I try to avoid the use of macros, so I actually don't know how to use them beyond the very most basic ones, but I'm trying to do some meta-manipulation so I assume macros are needed.
I have an enum listing various log entries and their respective id, e.g.
enum LogID
{
LOG_ID_ITEM1=0,
LOG_ID_ITEM2,
LOG_ID_ITEM3=10,
...
}
which is used within my program when writing data to the log file. Note that they will not, in general, be in any order.
I do most of my log file post-processing in Matlab so I'd like to write the same variable names and values to a file for Matlab to load in. e.g., a file looking like
LOG_ID_ITEM1=0;
LOG_ID_ITEM2=1;
LOG_ID_ITEM3=10;
...
I have no idea how to go about doing this, but it seems like it shouldn't be too complicated. If it helps, I am using c++11.
edit:
For clarification, I'm not looking for the macro itself to write the file. I want a way to store the enum element names and values as strings and ints somehow so I can then use a regular c++ function to write everything to file. I'm thinking the macro might then be used to build up the strings and values into vectors? Does that work? If so, how?

Answer 1

I agree with Adam Burry that a separate script is likely best for this. Not sure which languages you're familiar with, but here's a quick Python script that'll do the job:
#!/usr/bin/python
'''Makes a .m file from an enum in a C++ source file.'''
from __future__ import print_function
import sys
import re
def parse_cmd_line():
'''Gets a filename from the first command line argument.'''
if len(sys.argv) != 2:
sys.stderr.write('Usage: enummaker [cppfilename]\n')
sys.exit(1)
return sys.argv[1]
def make_m_file(cpp_file, m_file):
'''Makes an .m file from enumerations in a .cpp file.'''
in_enum = False
enum_val = 0
lines = cpp_file.readlines()
for line in lines:
if in_enum:
# Currently processing an enumeration
if '}' in line:
# Encountered a closing brace, so stop
# processing and reset value counter
in_enum = False
enum_val = 0
else:
# No closing brace, so process line
if '=' in line:
# If a value is supplied, use it
ev_string = re.match(r'[^=]*=(\d+)', line)
enum_val = int(ev_string.group(1))
# Write output line to file
e_out = re.match(r'[^=\n,]+', line)
m_file.write(e_out.group(0).strip() + '=' +
str(enum_val) + ';\n')
enum_val += 1
else:
# Not currently processing an enum,
# so check for an enum definition
enumstart = re.match(r'enum \w+ {', line)
if enumstart:
in_enum = True
def main():
'''Main function.'''
# Get file names
cpp_name = parse_cmd_line()
m_name = cpp_name.replace('cpp', 'm')
print('Converting ' + cpp_name + ' to ' + m_name + '...')
# Open the files
try:
cpp_file = open(cpp_name, 'r')
except IOError:
print("Couldn't open " + cpp_name + ' for reading.')
sys.exit(1)
try:
m_file = open(m_name, 'w')
except IOError:
print("Couldn't open " + m_name + ' for writing.')
sys.exit(1)
# Translate the cpp file
make_m_file(cpp_file, m_file)
# Finish
print("Done.")
cpp_file.close()
m_file.close()
if __name__ == '__main__':
main()
Running ./enummaker.py testenum.cpp on the following file of that name:
/* Random code here */
enum LogID {
LOG_ID_ITEM1=0,
LOG_ID_ITEM2,
LOG_ID_ITEM3=10,
LOG_ID_ITEM4
};
/* More random code here */
enum Stuff {
STUFF_ONE,
STUFF_TWO,
STUFF_THREE=99,
STUFF_FOUR,
STUFF_FIVE
};
/* Yet more random code here */
produces a file testenum.m containing the following:
LOG_ID_ITEM1=0;
LOG_ID_ITEM2=1;
LOG_ID_ITEM3=10;
LOG_ID_ITEM4=11;
STUFF_ONE=0;
STUFF_TWO=1;
STUFF_THREE=99;
STUFF_FOUR=100;
STUFF_FIVE=101;
This script assumes that the closing brace of an enum block is always on a separate line, that the first identifier is defined on the line following the opening brace, that there are no blank lines between the braces, that enum appears at the start of a line, and that there is no space following the = and the number. Easy enough to modify the script to overcome these limitations. You could have your makefile run this automatically.

Answer 2

Have you considered "going the other way"? It usually makes more sense to maintain your data definitions in a (text) file, then as part of your build process you can generate a C++ header and include it. Python and mako is a good tool for doing this.