- casting that's a lot of extra typing :-) - 17 Updates
- is there a C++ version of the strtok() function? - 2 Updates
- is there a C++ version of the strtok() function? - 2 Updates
| Bonita Montero <Bonita.Montero@gmail.com>: Jul 02 08:50AM +0200 >>> No. >> No, sure. > There is a difference between static_cast and reinterpret_cast. No? That wasn't the question. The question is if everything which can be done with C++-style casts can be done with C-style casts - and that's almost true. |
| Juha Nieminen <nospam@thanks.invalid>: Jul 02 08:14AM > C++-style casts are superfluous child-proof locks in most cases. > And in many cases they're even syntactic sugar. You could say that of the entirety of C++. Just program directly in asm. Heck, even asm is just syntactic sugar. Just program directly in machine code by writing the byte values into an executable file using a hex editor. |
| Bonita Montero <Bonita.Montero@gmail.com>: Jul 02 11:30AM +0200 >> And in many cases they're even syntactic sugar. > You could say that of the entirety of C++. Just program directly > in asm. That's an not fitting analogy. C++-style casts just don't have an advantage on the maintainability, deveopment-performance and ease of writing. |
| "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com>: Jul 02 12:20PM +0200 On 02.07.2019 11:30, Bonita Montero wrote: > That's an not fitting analogy. C++-style casts just don't have an > advantage on the maintainability, deveopment-performance and ease > of writing. I hate to agree with Juha, since he has adopted the sideline hobby of bashing me at any opportunity, but he's right. The `++` in C++ is nearly all about imposing constraints on the code, mostly via static typing, and the named casts help with that. For example, `static_cast` does a static cast and no other kind of cast. Cheers!, - Alf |
| Bart <bc@freeuk.com>: Jul 02 11:51AM +0100 On 02/07/2019 09:14, Juha Nieminen wrote: > Heck, even asm is just syntactic sugar. Just program directly in > machine code by writing the byte values into an executable file > using a hex editor. A hex editor? What luxury! I used LED lights to show binary contents of memory locations, and an earth lead to touch 8 metal contacts to set individual bits (couldn't afford so many push-buttons) to program in binary machine code. (This was actually quite true.) |
| Bonita Montero <Bonita.Montero@gmail.com>: Jul 02 01:25PM +0200 > The `++` in C++ is nearly all about imposing constraints on the > code, mostly via static typing, and the named casts help with that. No, they rarely make things more readable or maintainable. > For example, `static_cast` does a static cast and no other kind of cast. C++-style casts are mostly an idea for compulsive developers; and compulsiveness is an occupational illness of may developers. |
| Ben Bacarisse <ben.usenet@bsb.me.uk>: Jul 02 02:35PM +0100 >> using a hex editor. > A hex editor? What luxury! > I used LED lights to show binary contents of memory locations, <accent location=northern> LED lights? Luxury! Bloody luxury! When I were a lad we had to lick terminals on 't delay lines wi' our tongues to read memory. </accent> -- Ben. |
| Christian Gollwitzer <auriocus@gmx.de>: Jul 02 04:47PM +0200 Am 02.07.19 um 15:35 schrieb Ben Bacarisse: > LED lights? Luxury! Bloody luxury! When I were a lad we had to lick > terminals on 't delay ines wi' our tongues to read memory. > </accent> https://xkcd.com/378/ |
| James Kuyper <jameskuyper@alumni.caltech.edu>: Jul 02 07:59AM -0700 On Tuesday, July 2, 2019 at 9:35:21 AM UTC-4, Ben Bacarisse wrote: > Bart <bc@freeuk.com> writes: ... > LED lights? Luxury! Bloody luxury! When I were a lad we had to lick > terminals on 't delay lines wi' our tongues to read memory. > </accent> How far north? Greenlandic? :-) "Shadwell hated all Southerners, and by inference, was standing at the north pole." ("Good Omens" - Terry Pratchet). |
| G G <gdotone@gmail.com>: Jul 02 09:10AM -0700 James: Hahahahaha, that was funny. "...Standing at the North Pole...". ...hated all southerners ... Cause I had to read that twice . There is humor in this group. :- ) |
| James Kuyper <jameskuyper@alumni.caltech.edu>: Jul 02 10:06AM -0700 On Tuesday, July 2, 2019 at 12:10:23 PM UTC-4, G G wrote: > Hahahahaha, that was funny. "...Standing at the North Pole...". ...hated all southerners ... > Cause I had to read that twice . > There is humor in this group. :- ) It can be hard to be sure on usenet whether or not a comment is intended to be sarcastic unless it's specifically labelled as such - your wording gives me some doubt about it. If that wasn't sarcastic, I strongly recommend reading anything by Terry Pratchet - there's lots more where that came from, and that's far from being the funniest line he's written. |
| Melzzzzz <Melzzzzz@zzzzz.com>: Jul 02 05:38PM > That's an not fitting analogy. C++-style casts just don't have an > advantage on the maintainability, deveopment-performance and ease > of writing. Not true. -- press any key to continue or any other to quit... U ničemu ja ne uživam kao u svom statusu INVALIDA -- Zli Zec Na divljem zapadu i nije bilo tako puno nasilja, upravo zato jer su svi bili naoruzani. -- Mladen Gogala |
| Bonita Montero <Bonita.Montero@gmail.com>: Jul 02 07:48PM +0200 >> advantage on the maintainability, deveopment-performance and ease >> of writing. > Not true. No, true. ;-) |
| Vir Campestris <vir.campestris@invalid.invalid>: Jul 02 09:16PM +0100 On 02/07/2019 18:06, James Kuyper wrote: > gives me some doubt about it. If that wasn't sarcastic, I strongly > recommend reading anything by Terry Pratchet - there's lots more where > that came from, and that's far from being the funniest line he's written. Pratchett is always worth a read. You'll even notice he understands computer people - if you read about the clacks. Andy -- Who doesn't go past core store and dip switches - and that was only once... |
| G G <gdotone@gmail.com>: Jul 02 03:50PM -0700 > gives me some doubt about it. If that wasn't sarcastic, I strongly > recommend reading anything by Terry Pratchet - there's lots more where > that came from, and that's far from being the funniest line he's written. James: no i thought that was funny... really! i will look up Terry Pratchet. i've been watching amazon prime stuff lately, and have found Canadian tv very funny, the last few days. so i was in the comedic mindset when i read it i guess. comedies like : amazon: corner gas, youtube: little mosque on the prairie , bbc: yes minister and yes prime minister. who knew canada could tell a good joke (just kidding about canada telling a good joke) those shows have me laughing out loud. yes i enjoyed the joke. no sarcasm here. |
| "Chris M. Thomasson" <invalid_chris_thomasson_invalid@invalid.com>: Jul 02 03:51PM -0700 On 7/2/2019 1:14 AM, Juha Nieminen wrote: > Heck, even asm is just syntactic sugar. Just program directly in > machine code by writing the byte values into an executable file > using a hex editor. The Woz! :^) |
| "Chris M. Thomasson" <invalid_chris_thomasson_invalid@invalid.com>: Jul 02 03:52PM -0700 On 7/2/2019 6:35 AM, Ben Bacarisse wrote: > LED lights? Luxury! Bloody luxury! When I were a lad we had to lick > terminals on 't delay lines wi' our tongues to read memory. > </accent> LOL! :^D |
| alexo <alelvb@inwind.it>: Jul 02 07:59PM +0200 Il 02/07/19 19:06, Stefan Ram ha scritto: >> CuSO4*5H2O > I do not know how crystallization should be parsed, > therefore, I ignored crystallization. take for example CuSO4*5H2O the number 5 following the '*' character is the number of molecules that follow it, in that case H2O, so the parser should read 10 Hydrogen atoms 5 Oxygen atoms > How to do this evaluation depends on the kind of evaluation > wanted here. I don't know what kind of evaluation is wanted > here. I'm Sorry but I don't know what a syntax tree is. I know what an informatic tree is but I never implemented one myself. I've published the code of my parser in the hope that someone could suggest me improves, but I think that the group thinks I'm a lazy student :( but that's not so. I'm not a student anymore. I've had my laurea in chemistry 19 years ago. I have to say moreover that I didn't understand the code you wrote some days ago. It's full of things I don't yet know. But as I've already told it works. Anyway a big thank you for your interest. alessandro |
| alexo <alelvb@inwind.it>: Jul 02 09:52PM +0200 Il 02/07/19 20:22, Stefan Ram ha scritto: > [.. code omitted ..] that is amazing! Progrmming is amazing! --- Warning --- personal history follows. if you are not interested in my life, skip reading further. You've been advised ;) When I was a kid my grandpa bought me a C64. I live in Italy and at that times I was about 7 or 8 years old. I remember that besides the games that I never ended, I tried to make some BASIC code programs working, but with no or few success. I was always making transcription errors. Moreover the instructions were in English - I couldn't speak nor read it yet, and those listings were not 'Hello world' programs, but several pages long and I never had the satisfaction of making something of them working. So my experience with computers was initially frustrating. When I chose the university faculty, I opted for chemistry, but it was only at the 3rd year (in 1997) that I had the possibility to study a programming language. It was Fortran77 - the teacher was not up-to-date in the IT world - and that language even if old, opened me a world. But it was too late. My study road was at half a half and it was late to change. But what remained from that days was the passion. My first 'hobbyist' programming attempts are dated back to the very first years of 2000's whit Java. But my step were: learning a bit of Java -> learning a bit C -> learning C++ (still in progress) Mr Stroustrup writes that it's not necessary to learn C before learning C++ but to me was nonsense learning OO programming (that anyway uses structured statements) without knowing anything about structured programming. And Java was born to avoid pointers that are essential in C and C++. So since this languages share the same syntax I wanted to know more about C. Now java is set aside, but I feel still at a beginner level both with C and C++. I know a bit about linked lists and I've read two sorting algorithms merge and quick sort. actually I've written two GUI interfaces in FLTK and a few more things Even if I read of programming from about 20 years I have to admit that I'm not constant in writing code nor in the point were I'm. My parser was a brute-force approach. It reads the formula left to right like a human does. and recursively calls itself to analyze blocks inside parentheses. But something is not working as I expected. Maybe I'll be able to fix it or maybe not. It doesn't matter. Its a hobby. thank to you all in the group. |
| ram@zedat.fu-berlin.de (Stefan Ram): Jul 02 05:06PM >But to be perfect it should handle even the molecules of crystallization >that are written in this way (but I didn't talk about them in my post: >CuSO4*5H2O I do not know how crystallization should be parsed, therefore, I ignored crystallization. In the meantime, I have developed another idea: We parse to build a syntax tree in memory and then evaluate the syntax tree somehow. But a formula like "[Fe(CO)6][Sb2F11]2" already /is/ a syntax tree from a certain point of view. So, I wonder whether a parser is needed at all! Instead, one can just decorate the tree with some functions for traversal and then start to do the evaluation directly on this tree which is given as (for example) "[Fe(CO)6][Sb2F11]2". How to do this evaluation depends on the kind of evaluation wanted here. I don't know what kind of evaluation is wanted here. |
| ram@zedat.fu-berlin.de (Stefan Ram): Jul 02 06:22PM >I'm Sorry but I don't know what a syntax tree is. I know what an >informatic tree is but I never implemented one myself. A syntax tree (usually called "abstract syntax tree", AST) is an internal representation of the structure of parsed text. >I have to say moreover that I didn't understand the code you wrote some >days ago. It's full of things I don't yet know. But as I've already told >it works. I wrote a small tutorial about parsing in C, here it is: (If answering to this following post, one should please not quote all of it, but only a few lines one directly refers to.) In order to interpret or translate an expression (term), it is decomposed into lexical units (tokens, words), which then are used by a parser to build symbols and a structured representation of the input. This representation then might be evaluated or translated into some other representation. The syntactial structuring resembles the rules for the construction of an expression, which often is given by so- called "productions" of the EBNF (extended Backus-Nauer-Form) and which sometimes are left-recursive. When writing a parser, the left-recursive productions sometimes are a worry to the author, because it is not obvious how to avoid an infinite recursion. The solution is to rewrite them as right-recursive productions. The addition with a binary infix Operator, for example, is left associative. However, it is simpler to analyze in a right-associative manner. Therefore, one analyzes the source using right-associative rules and then creates a result using a left-associative interpretation. A left-associative grammar might be, for example, as follows. <numeral> ::= '2' | '4' | '5'. <expression> ::= <numeral> | <expression> '+' <numeral>. start symbol: <expression>. To analyze this using a recursive descent parser, one prefers to use the following grammar. <numeral> ::= '2' | '4' | '5'. <expression> ::= <numeral>[ '+' <expression> ]. start symbol: <expression>. This can be written using iteration as follows. <numeral> ::= '2' | '4' | '5'. <expression> ::= <numeral>{ '+' <numeral> }. start symbol: <expression>. However, the product is created in the sense of the first grammar. Example code follows. #include <stdio.h> /* printf */ /* scanner */ static inline char get() { static char const * const source = "2+4+5)"; static int pos = 0; return source[ pos++ ]; } /* parser */ static inline int numeral(){ return get() - '0'; } static int sum(){ int result = numeral(); while( '+' == get() )result += numeral(); return result; } /* main */ int main( void ){ printf( "sum = %d\n", sum() ); } To be able to parse expressions with higher priority, the grammar can be extended. <numeral> ::= '2' | '4' | '5'. <product> ::= <numeral> | <product> '*' <numeral>. <sum> ::= <product> | <sum> '+' <product>. start symbol: <sum>. In iterative notation: <numeral> ::= '2' | '4' | '5'. <product> ::= <numeral>{ '*' <numeral> }. <sum> ::= <product>{ '+' <product> }. start symbol: <sum>. In C: #include <stdio.h> /* printf */ /* scanner */ static inline char get( int const move ) { static char const * const source = "2+4*5)"; static int pos = 0; char result = source[ pos ]; pos += move; return result; } /* parser */ static inline int numeral(){ return get( 1 )- '0'; } static int product(){ int result = numeral(); while( '*' == get( 0 )){ get( 1 ); result *= numeral(); } return result; } static int sum(){ int result = product(); while( '+' == get( 1 ))result += product(); return result; } /* main */ int main( void ){ printf( "sum = %d\n", sum() ); } Exercises - What is the output of the above programs? - Extend the last grammar and the last program so as to handle subtraction. - Extend the result of the last exercise in order to handle division. - Extend the result of the last exercise so that also numbers with multiple digits are accepted. - Extend the result of the last exercise so that also terms in parentheses are accepted. The input "(2+4)*5)" should give the result "30". - Extend the result of the last exercise so that also a unary minus "-" is recognized. - Extend the result of the last exercise so that more operators and functions are recognized. - Extend the result of the last exercise so that meaningful error messages are created for all inputs that do not fulfill the rules of the input language. - Extend the result of the last exercise so that the error messages also show the location where the error was detected. It should be possible to enter an expression that spans multiple lines, and an error message should contain the number of the line where the error was detected. See also: http://compilers.iecc.com/crenshaw/ So far for the small C parser tutorial. I also wrote a C++ parser in the spirit of the above C parser that uses special features of C++. But this code is more compact and therefore possibly more difficult to understand. #include <iostream> #include <ostream> #include <map> #include <functional> #include <cmath> #include <sstream> #include <cstring> ::std::map< char, ::std::function< double( double, double )>> ex { { '^', []( double const x, double const y )->double { return ::std::pow( x, y ); }}, { '*', []( double const x, double const y )->double{ return x * y; }}, { '/', []( double const x, double const y )->double{ return x / y; }}, { '+', []( double const x, double const y )->double{ return x + y; }}, { '-', []( double const x, double const y )->double{ return x - y; }}}; ::std::map< char, bool >left_associative { { '^', false }, { '*', true }, { '/', true }, { '+', true }, { '-', true }}; template< typename scanner >struct parser { scanner s; parser( char const * s ): s{ s } {} char check( char const * const op ) { return ::std::strchr( op, static_cast< char >( s.peek() )) ? static_cast< char >( s.get() ): 0; } double numeral(){ return s.get() - '0'; } double prefix(){ int sign = 1; while( '-' == s.peek() ){ s.get(); sign *= -1; } return sign * numeral(); } double parse( char const * const op, double( ::parser< scanner >::*next ) () ) { double result =( this->*next )(); for( char sym; sym = check( op ); )result = ex[ sym ] ( result, left_associative[ sym ]?( this->*next )(): parse( op, next )); return result; }; double power(){ return parse( "^", &::parser< scanner >::prefix ); } double product(){ return parse( "*/", &::parser< scanner >::power ); } double sum(){ return parse( "+-", &::parser< scanner >::product ); } double start(){ return sum(); }}; int main() { using p = ::parser< ::std::stringstream >; auto test = []( char const * s ){ ::std::cout << p{ s }.start() << '\n'; }; test( "2^2^3/2/2" ); test( "2+2*2^2^-3" ); } But both example parsers do not actually build a syntax tree in memory but rather evaluate the given expression. A (binary) tree is a value that might contain pointers to two other trees: the left subtree and the right subtree. One can imagine it like 3 / \ / \ 1 4 / \ / \ 0 2 (in compact notation: »(((0)1(2))3(4))«). It can be build in C as typedef struct tree { struct tree * left; int value; struct tree * right; } * TREE; extern struct tree t1, t0, t2, t4; struct tree t3 = { &t1, 3, &t4 }, t1 ={ &t0, 1, &t2 }, t4 ={ 0, 4, 0 }, t0 ={ 0, 0, 0 }, t2 ={ 0, 2, 0 }; Now, the three is »t3«. A program that actually builds a tree in memory from a tree expression given at runtime can look like #include <stdio.h> /* printf, putchar */ #include <stdlib.h> /* EXIT_SUCCESS, abort */ /* tree */ typedef struct tree { struct tree * left; int value; struct tree * right; } * TREE; TREE newtree( TREE const left, int const value, TREE const right ) { TREE const result = malloc( sizeof *result ); if( !result )abort(); result->left = left; result->value = value; result->right = right; return result; } /* scanner */ char get( int const move ) { static char const * const source = "(((0)1(2))3(4))"; static int pos = 0; char const result = source[ pos ]; if( result )pos += !!move; return result; } /* parser */ int number( void ){ return get( 1 )- '0'; } TREE tree( void ); TREE entry( void ) { TREE left, right; int value; get( '(' ); left = tree(); value = number(); right = tree(); get( ')' ); return newtree( left, value, right ); } TREE tree( void ) { return get( 0 )== '(' ? entry() : 0; } /* serializer */ void print( const TREE const tree ) { if( tree ) { putchar( '(' ); print( tree->left ); printf( "%d", tree->value ); print( tree->right ); putchar( ')' ); }} /* main */ int main( void ) { print( tree() ); putchar( '\n' ); return EXIT_SUCCESS; } |
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