I'm working on a project and have a problem that I believe can be solved with macros, but given the nature of the issue I don't have the experience to write one myself.
Here's what I would expect as input and output of the #define macro:
Inputting code such as this
printf(foobar(Hello World.));
Should result in the preprocessor producing code that reads:
printf((char *)(std::string("")+'H'+'e'+'l'+'l'+'o'+' '+'W'+'o'+'r'+'l'+'d'+'.').c_str());
I'm assuming something this complicated is possible, and I hope one of you guys can help me out.
I NEED IT TO BE A MACRO, I DO NOT want a string constant anywhere.
The only solution I can think of is to run your code through a suitable script (probably just some light awk), that does the substitution before your code reaches the pre-compiler.
Depending on your environment you could do this as a "Pre-Build Event" in Visual Studio, or just add a step directly into your makefile.
Uh, I fear it is impossible (unless I don't know something).
I believe there is no macro to split a given input token (e.g. Hello) into characters building it (H e l l o)
There were some attempts to do such thing, but I fear it is not exactly what you need:
C++: Can a macro expand "abc" into 'a', 'b', 'c'?
"More powerful precompiler" ?
Try this topic: Replacements for the C preprocessor
Macros are basically substitution or addition of strings.
You could do this with a pre-processor of your own, but the standard pre-processor won't split strings into component parts.
How about this:
Put all these (assuming there is more than one) 'macros' in a separate file. Write a program that translates them into the expansion you require and then include THAT file in your c program? You could then make the expansion program part of your make file so it's always up to date.
Using a separate file makes the expansion program much easier than parsing a c/c++ file.
Since you're looking for a narrow, direct answer to your question and without suggestions, here goes:
This is impossible. You must find a different solution to whatever it is you're trying to achieve.
Have you tried:
#define toString(x) #x
You can use it after like this:
printf("%s", toString(hello world));
Don't try to use printf directly with the string because you can have format specifier in the string.
printf(toString(hello world)); //wrong, you can have for example %d in the string
Related
I want to write a program that takes an string like x^2+1 and understand it.
I want to ask the user to enter her/his function and I want to be able to process and understand it. Any Ideas?
char s[100];
s <- "x*I+2"
x=5;
I=2;
res=calc(s);
I think it could be done by something like string analyses but I think Its so hard for me.
I have another Idea and that is using tcc in main program and doing a realtime compile and run and delete a seprated program (or maybe function) that has the string s in it.
and I will create a temp file every time and ask tcc to compile it and run it by exec or similar syntax.
/*tmp.cpp:*/
#include <math.h>
void main(/*input args*/){
return x*I+2;
}
the tmp.cpp will created dynamically.
thanks in advance.
I am not sure what do you expect. It's too complex to give the code as answer, but the general idea is not very complex. It's not out of reach to code, even for a normal hobbyist programmer.
You need to define grammar, tokenize string, recognize operators, constants and variables.
Probably put expression into a tree. Make up a method for substituting the variables... and you can evaluate!
You need to have some kind of a parser. The easiest way to have math operations parsable is to have them written in RPN. You can, however, write your own parser using parser libraries, like Spirit from boost or Yacc
I use with success , function parser
from www it looks like it supports also std::complex, but I never used it
As luck would have it, I recently wrote one!
Look for {,include/}lib/MathExpression/Term. It handles complex numbers but you can easily adapt it for plain old floats.
The licence is GPL 2.
The theory in brief, when you have an expression like
X*(X+2)
Your highest level parser can parse expressions of the form A + B + C... In this case A is the whole expression.
You recurse to parse an operator of higher precedence, A * B * C... In this case A is X and B is (X+2)
Keep recursing until you're parsing either basic tokens such as X or hit an opening parenthesis, in which case push some kind of stack to track where your are and recurse into the parentheses with the top-level low-precedence parser.
I recommend you use RAII and throw exceptions when there are parse errors.
use a Recursive descent parser
Sample: it's in german, but a small and powerfull solution
look here
here is exactly what You are searching for. Change the function read_varname to detect a variable like 'x' or 'I'.
I would like to do some debugging of my crazy macros, but there's no way to do it because macros generate code, not strings. I'd have to change the macros to emit strings in order for my program to print out the code that it would otherwise produce.
New in C++11 are R"delim("Raw Strings")delim", and I was hoping that there is some way to interpolate code-macros inside of one of these to turn that code into a string literal.
Raw string literals concatenate the same way as normal string literals.
#define MYMACRO "hello"
std::string blah = R"(first part -)" MYMACRO R"(- second part)";
std::cout << blah;
will output first part -hello- second part
If you want to debug your crazy macros, you'd probably get more mileage out of directly examining the preprocessed output. Any C/C++ compiler will have an option for this. In GCC it's -E; for MSVC, I don't recall where it is exactly, but one of the properties sections has "keep preprocessed output". When you do this, keep your #includes to a minimum, especially standard-library #includes; these can add hundreds or thousands of lines of code to the top of the preprocessed output.
I'm working with very large integer literal defines eg:
#define X 999999999999
To improve readability I tried changing this to:
#define X 999/**/999/**/999/**/999
But the compiler was like "nah bru.."
Is there any way to make these more readable?
Just to clarify, this question is asking only about the appearance of the values in the source code. I'm not asking how to format these values in a printf or anything.
You can do this in a define (but not outside of a define):
#define X 999##111##333##444
I'm not sure that I'd recommend it, but it's legal. (## is the preprocessor token concatenation operator.)
You explicitly didn't ask about output formatting, so you're probably not interested in input formatting either, but both of them can be made locale-aware, which includes allowing locale-specific grouping characters.
You could do this:
#include <boost/preprocessor.hpp>
BOOST_PP_SEQ_CAT((345)(678)(901))
Which would show up in source code as:
345678901
I have a lot of "stupid" #define in a project and I want to remove them. Unfortunately, I can't do a simple search and replace, since the #define is parameterized. For example:
#define FHEADGRP( x ) bool _process_grp##x( grp_id_t , unsigned char )
This is used to generate headers of a couple of functions. I would like to somehow do the same thing as the preprocessor does - replace each call of the macro by its result (with correct parameters inserted. I hope you understand what I want to do.
I found out that with Visual Studio, one can get the preprocessed intermediate files with the /P option. Unfortunately, this does not help me, since the file is "polluted" with thousands of other lines and with all #defines expanded. I do not want to do this, I just want to expand some of the macros and preferably do it in my IDE (which is Visual Studio). Is there any way how to achieve this?
You can normally get the output of the preprocessor with gcc -E (assuming you're using gcc of course, though other compiler tend to have the same feature).
Of course, processing that file to automatically expand the #define's into other text is not a trivial task. I'd probably write a shell script (or Perl since it's a lot better at massaging text in my opinion) to automate the task.
In Visual Studio, you can use /P to perform the same operation. This can be set in the IDE according to this page.
Yes, there is - since you're using Visual Studio.
The Visual Studio IDE has a powerful search & replace mechanism. You seem to assume it can only handle literal strings. It can do more. Hit Ctrl-Shift-H for a global search and replace. In the "Find options", select "Use: Wildcards".
Now replace FHEADGRP(*) by bool _process_grp\1( grp_id_t , unsigned char )
The wildcard is *, and \1 is the backreference.
[edit]
Macros work on the tokenized source, but Search&Replace works on characters. This can cause a slight problem. Consider the cases FHEADGRP(Foo) and FHEADGRP( Foo ). For a C macro, they're equivalent, but in the second case the backreference will expand to Foo - with spaces.
The workaround is to use regexes, in particular replace FHEADGRP\(:b*(.*):b*\) with bool _process_grp\0( grp_id_t , unsigned char ). I find that the VS2005 implementation is a bit buggy; for instance the simple ? expression fails to match a single space. But the example above should work.
Uh I would advise you to use sed, http://www.gnu.org/software/sed/, or another regex tool.
Presently I have a some legacy code, which generates the op code. If the code has more number of macros then the code generation takes so much of time (In terms of hours!!).
I have gone through the logic, they are handling the macro by searching for it and doing a replace of each variable in it some thing like inlining.
Is there a way that I can optimize it without manipulating the string?
You must tokenize your input before starting this kind of process. (I can't recommend the famous Dragon Book highly enough - even the ancient edition stood the test of time, the updated 2006 version looks great). Compiling is the sort of job that's best split up into smaller phases: if your first phase performs lexical analysis into tokens, splitting lines into keywords, identifiers, constants, and so on, then it's much simpler to find the references to macros and look them up in a symbol table. (It's also relatively easier to use a tool like lex or flex or one of their modern equivalents to do this job for you, than to attempt to do it from scratch).
The 'clue' seems to be if the code has more number of macros then the code generation takes so much of time. That sounds like the process is linear in the number of macros, which is certainly too much. I'm assuming this process occurs one line at a time (if your language allows that, obviously that has enormous value, since you don't need to treat the program as one huge string), and the pseudocode looks something like
for(each line in the program)
{
for(each macro definition)
{
test if the macro appears;
perform replacement if needed;
}
}
That clearly scales with the number of macro definitions.
With tokenization, it looks something like this:
for(each line in the program)
{
tokenize the line;
for(each token in the line)
{
switch(based on the token type)
{
case(an identifier)
lookup the identifier in the table of macro names;
perform replacement as necessary;
....
}
}
}
which scales mostly with the size of the program (not the number of definitions) - the symbol table lookup can of course be done with more optimal data structures than looping through them all, so that no longer becomes the significant factor. That second step is something that again programs like yacc and bison (and their more modern variants) can happily generate code to do.
afterthought: when parsing the macro definitions, you can store those as a token stream as well, and mark the identifiers that are the 'placeholder' names for parameter replacement. When expanding a macro, switch to that token stream. (Again, something things like flex can easily do).
I have an application which has its own grammer. It supports all types of datatypes that a typical compiler supports (Even macros). More precisely it is a type of compiler which generates the opcodes by taking a program (which is written using that grammer) as input.
For handling the macros, it uses the text replacement logic
For Example:
Macro Add (a:int, b:int)
int c = a + b
End Macro
// Program Sum
..
int x = 10, y = 10;
Add(x, y);
..
// End of the program
After replacement it will be
// Program Sum
..
int x = 10, y = 10;
int c = x + y
..
// End of program
This text replacement is taking so much of time i.e., replacing the macro call with macro logic.
Is there a optimal way to do it?
This is really hard to answer without knowing more of your preprocessor/parse/compile process. One idea would be to store the macro names in a symbol table. When parsing, check text tokens against that table first, If you find a match, write the replacement into a new string, and run that through the parser, then continue parsing the original text following the macrto's close parens.
Depending on your opcode syntax, another idea might be - when you encounter the macro definition while parsing, generate the opcodes, but put placeholders in place of the arguments. Then when the parser encounter calls to the macro, generate the code for evaluating the arguments, and insert that code in place of the placeholders in the pre-generated macro code.