ATL / WTL / STL

4-Feb-19 3:55

Oh, wow, that's a pretty neat trick! Thanks for the suggestion.

Richard MacCutchan4-Feb-19 4:04

Can a union in standard C "skip" members?

4-Feb-19 4:04

You're welcome.

Business2sell18-Feb-19 18:08

Business2sell

18-Feb-19 18:08

Good work..!!

arnold_w31-Jan-19 22:46

31-Jan-19 22:46

The following is an example of a simple struct union:

C++

typedef union _UINT32_PART_ {
   uint32_t dwWord;

   struct {
      uint16_t dwMSB;
      uint16_t dwLSB;
   } hw;

   struct {
      uint8_t byMSB;
      uint8_t byMSBL;
      uint8_t byLSBH;
      uint8_t byLSB;
   } b;
} DWORD_PART;

Is is possible to somehow omit, for example dwMSB and byLSBH, without making the subsequent members point to the wrong things? So, basically this is what I want:

C++

typedef union _UINT32_PART_ {
   uint32_t dwWord;

   struct {
                         // 2 bytes empty gap
      uint16_t dwLSB;    // This must still point to the 2nd word, not the 1st!
   } hw;

   struct {
      uint8_t byMSB;
      uint8_t byMSBL;
                         // 1 byte empty gap
      uint8_t byLSB;     // This must still point to the 4th byte, not the 3rd!
   } b;
} DWORD_PART;

Richard MacCutchan31-Jan-19 23:18

31-Jan-19 23:18

No, and what would be the point?

arnold_w31-Jan-19 23:47

31-Jan-19 23:47

To divide a struct into a high-level application level part and a low-level driver part.

Richard MacCutchan31-Jan-19 23:52

31-Jan-19 23:52

Sorry, but I do not understand what you hope to achieve. A struct is just a description of a block of memory that contains a fixed set of bytes, words etc. If it is 20 bytes long then you must describe each part exactly so the compiler can calculate the offsets correctly. Leaving blank space and expecting the compiler to guess what is missing makes no sense.

arnold_w1-Feb-19 0:13

1-Feb-19 0:13

Yes, but just like you can choose to only initialize parts of a struct:

C++

struct demo_s {
  int     first;
  int     second;
  int     third;
};
struct demo_s demo2 = { .second = 2, .third = 3 };

I was hoping that some union names (hw or b, in the example in my first post) could omit having a reference.

Richard MacCutchan1-Feb-19 1:42

1-Feb-19 1:42

Whether you initialise all or part of the struct before using it does not matter, except for your code. But you must still define it exactly and completely.

arnold_w1-Feb-19 2:08

1-Feb-19 2:08

Yes, but only struct members relevant to the application level should be initialized at the application level. The low-level driver struct members should be initialized at the low-level driver level.

Richard MacCutchan1-Feb-19 2:57

1-Feb-19 2:57

That is irrelevant; this discussion is about the struct definition. What you do with the content is dependent on your code, but the definition (as I keep repeating) must include every element of the block of memory.

Message Closed

16-Apr-20 20:04

xiaofeifei66

16-Apr-20 20:04

Message Closed

Which type of Regex best to learn for programming with C?

0x01AA5-Jan-22 4:30

0x01AA

5-Jan-22 4:30

Your first union does the job.
So maybe you give "uint8_t byLSBH;"another name to make it clear it is not relevant?

HS_C_Student17-Dec-18 3:43

HS_C_Student

17-Dec-18 3:43

I like C but I feel it's Achilles heel is string processing. I've started to do a lot of parsing of text databases in arbitrary format without documentation lately and I need to adapt.

What I need to do is define patterns - expected format for the data and to store the values only if the whole string matches that known pattern. Input validation.

I'd rather not run the rest of my code without verifying the input conforms.

I think regular expressions are the best way to augment my existing skills without learning a new language, but regexes seem kind of varied and mixed breed.

Perl (5?) Seems to have formal standardization of regexes which is supported in many searching and text editing programs. There's also PCRE which I can compile on windows or download precompiled lib/dll.

Should I learn Perl regexes and use PCRE or am I overlooking things?

Re: Which type of Regex best to learn for programming with C?

Richard MacCutchan17-Dec-18 3:53

Re: Which type of Regex best to learn for programming with C?

17-Dec-18 3:53

There are many websites that help to learn regexes, Expresso Regular Expression Tool[^] is a popular one. But you will also need a support library, as C does not have native support for them.

HS_C_Student17-Dec-18 5:57

HS_C_Student

17-Dec-18 5:57

As far as I can tell there are at least three main types; POSIX basic, POSIX extended, and Perl Compatible.

There's a list of engines here:

Comparison of regular expression engines - Wikipedia[^]

And apparently some differences between PERL and PCRE:

Perl Compatible Regular Expressions - Wikipedia[^]

I don't know/understand if let's say 80 or 97 percent of the Regex syntax is the same between one version or another or if they are distinct subtypes with significant differences.

I don't know if they all support ascii, Unicode, and utf encoding, or whether they are all capable of returning matched variables or if some are only providing a match/no match result.

Re: Which type of Regex best to learn for programming with C?

Richard MacCutchan17-Dec-18 6:48

Re: Which type of Regex best to learn for programming with C?

17-Dec-18 6:48

You will have to read the documentation to find out which one suits your requirements best.

John R. Shaw9-Jan-20 20:50

John R. Shaw

9-Jan-20 20:50

PCRE is a good option. It is based on the Perl regexe, although there are some minor differences under the hood (which I do not remember now). I wrote my own C++ template regex some years ago that gives me full control of behavior in my personal projects. I used other libraries like PCRE, for comparison, in my test bed, to test for speed and accuracy. That is why I know that there are some minor differences on what one considers valid and invalid syntax (implementation differences or programmers mind set - who knows?).

As for Cs ability to process strings or any other data type - it is very efficient. I used to be able to look a C-code and translate it, in my head, directly to the equivalent assembly code. What you are talking about is the standard C libraries, which were designed to provide only the simple low level functionality that programmers require to develop more complex algorithms (how many ways are there to write a 'strcmp' function?). It was left to others to provide libraries that required more than a simple 'for' or while 'loop' in their functions.

That being said, when I find my self doing contract work on old C-code, where I am not allowed to upgrade or use external libraries, I recreate some simple algorithms for parsing (hey its their money, so who am I to argue with a brick wall). Basically, I create equivalent functions for parsing sub-strings like the regex "\d*" or "[abd]" and wrap them in a function call - depending on what I am looking for. What little testing I have done has actually shown me that they were more efficient than using the MS implementation of regex (not a surprise).

Conclusion: C is the most efficient language I have ever work with - there is a reason that all of the modern operating systems, I have worked with, were written in C. (I have not checked lately, so it is possible that C++ snuck in their some were).

INTP
"Program testing can be used to show the presence of bugs, but never to show their absence." - Edsger Dijkstra
"I have never been lost, but I will admit to being confused for several weeks. " - Daniel Boone

Directory manipulation in C++

tasumisra16-Oct-18 4:26

tasumisra

16-Oct-18 4:26

Dear Friends,

I am working on a legacy project where i do not have support for boost libraries or latest C++ version.

I need to identify the path of a file with given extension(*.abc) that is inside couple of folder.

as example i have path like C:\test

but the given file is found in c:\test\Application\SomeohterApplication\hello.abc

can someone help please ?

Thanks in advance.

vikas da

Re: Directory manipulation in C++

Richard MacCutchan16-Oct-18 4:34