Re: design question : variadic functions use ? . - C / C++ / MFC Discussion Boards

design question : variadic functions use ? .

Maximilien19-Dec-23 2:34

19-Dec-23 2:34

(probably a TOmato vs toMAto kind of questions... )

At what point should I use variadic functions vs. keeping it local ?

I have a library that handles SQL queries.

is there a difference between something like :

(overly simplified)

C++

// do the formatting before calling the function.
std::string fullyFormedQuery = sprintf (queryFormat, param1, param2, ... ); 
void DoRequest( std::string fullyFormedQuery){ 
  // call SQL with the fullyFormedQuery
} 

// do the formatting in the function.
void DoRequest( std::string queryFormat, param1, param2, ... ){ 
  std::string fullyFormedQuery= queryFormat(format, param1, param2, ... ); 
  // call SQL ... 
}

CI/CD = Continuous Impediment/Continuous Despair

Re: design question : variadic functions use ? .

Mircea Neacsu19-Dec-23 2:42

Mircea Neacsu

19-Dec-23 2:42

As you say it's more of a style question. My preference would be for the first option (pass fully formed string) because:
- there is less documenting to do
- some compilers (MSVC for one), check matching between format strings and parameters in (s)printf functions but don't do that in a user defined variadic function.

Mircea

Re: design question : variadic functions use ? .

Maximilien19-Dec-23 2:54

Maximilien

19-Dec-23 2:54

thanks.

CI/CD = Continuous Impediment/Continuous Despair

Re: design question : variadic functions use ? .

jschell19-Dec-23 5:08

jschell

19-Dec-23 5:08

Just noting that your examples leave out using bind variables.

My understanding, and I just googled to see if that seems to be correct, is that bind variables make optimizations in the database easier.

Not to mention of course that they are a better fit for avoiding SQL injection problems.

Setting up bind variables is rather complex so putting it in the method is going to be better.

Re: design question : variadic functions use ? .

Maximilien19-Dec-23 7:36

Maximilien

19-Dec-23 7:36

Thanks.

We already have a complete (decades old) framework for SQL. (seems to be working fine)

maybe I should have left out the SQL reference and make it a more generic question.

CI/CD = Continuous Impediment/Continuous Despair

Re: design question : variadic functions use ? .

jschell20-Dec-23 5:31

jschell

20-Dec-23 5:31

Maximilien wrote:
complete (decades old) framework for SQL.

Then you should use the same idiom as the existing code. Changing it for some and not others just adds to the confusion. Although if a preference for one is given and there is a large amount of new work (new files not modifying existing code) then maybe go with there.

modified 20-Dec-23 12:00pm.

Re: design question : variadic functions use ? .

Maximilien20-Dec-23 6:55

Maximilien

20-Dec-23 6:55

I will not change existing code; it's just too dangerous.

I'm just curious; if there's a best practice.

CI/CD = Continuous Impediment/Continuous Despair

Re: design question : variadic functions use ? .

jschell21-Dec-23 3:31

jschell

21-Dec-23 3:31

My best practice doesn't fit either of your suggestions...

If I am creating a new database layer (which I have numerous times) then the caller would never provide the SQL.

If the business layer(s) need new database logic then the database layer should be modified to provide it.

The caller provides the parameters that would be used in the call.

Then within that database layer method it would decide how to process the parameters and SQL (provided by the method.)

So it looks like the following.

void DatabaseDoX(param1, param2,...)
{
// multiple variations possible
std::string fullyFormedQuery = sprintf (SQL_X, param1, param2, ... );

There are quite a few variations on the above. For example consider the complication of a user initiated call where they might specify different 'query' terms (like data range, customer name, etc)

But all still hide the SQL.

Certainly there are design considerations for example your code might be coming from within the database layer (not a business call at all.) If so then I suspect that usage would actually vary depending on what the database layer was specifically doing in the code path.

strcpy_s weirdness

mike741119-Dec-23 1:31

mike7411

19-Dec-23 1:31

I was playing around in Microsoft Visual C++, and I noticed something weird about this code:

C++

void setname(char name[80])
{
    strcpy_s(name, "joebob");

    char name2[80];
    strcpy_s(name2, "joebob");
}

It looks like the compiler complains about the first strcpy_s but not the second one. If I comment out the first one, the program compiles fine.

Can anyone explain this?

BTW, I know strcpy_s should probably take 3 arguments, but I'm trying to understand this weirdness.

Thanks.

Re: strcpy_s weirdness

Mircea Neacsu19-Dec-23 1:43

Mircea Neacsu

19-Dec-23 1:43

Remember that in C arrays and pointers are the same thing so the argument name is a pointer to char. For the compiler, your code fragment is the same as:

C++

void setname(char *name)
{
    strcpy_s(name, "joebob");

    char name2[80];
    strcpy_s(name2, "joebob");
}

In the case of the second call to strcpy_s, the compiler can figure out the size parameter through some template magic. For the first one however you have to use the explicit size form.

Mircea

Re: strcpy_s weirdness

Richard MacCutchan19-Dec-23 2:04

Richard MacCutchan

19-Dec-23 2:04

It would help when posting questions that you include the exact error message(s), so it makes it clear what your problem is.

Re: strcpy_s weirdness

CPallini19-Dec-23 2:09

CPallini

19-Dec-23 2:09

See, for instance
Array Decay In C - GeeksforGeeks[^].

"In testa che avete, Signor di Ceprano?"
-- Rigoletto

Should this work in C++?

mike741118-Dec-23 7:07

mike7411

18-Dec-23 7:07

Should this work in C++?

C++

long add1(a)
 long a;
 {
 return a+1;
 }

It doesn't seem to compile in Visual Studio. I got it from MIT's OpenCourseware.

Thanks.

Re: Should this work in C++?

Mircea Neacsu18-Dec-23 7:17

Mircea Neacsu

18-Dec-23 7:17

That is the so called K&R syntax[^]. You can compile as C code but not as C++. The C++ version would be:

C++

long add1 (long a) {
  return a+1;
}

Mircea

Re: Should this work in C++?

Maximilien19-Dec-23 5:11

Maximilien

19-Dec-23 5:11

mike7411 wrote:
I got it from MIT's OpenCourseware.

I see the MIT is still at the cutting edge of technology !! Roll eyes | :rolleyes:

CI/CD = Continuous Impediment/Continuous Despair

C++ memory freeing

mike741116-Dec-23 3:04

mike7411

16-Dec-23 3:04

I am a little confused about when to use delete and delete[].

Is this correct?

C++

int* numArray = new int[100];
delete numArray;

Or should it be this?

C++

int* numArray = new int[100];
delete[] numArray;

I saw the former in an MIT lecture, and it looked suspicious. Both of them compile.

Thanks.

Re: C++ memory freeing

Richard MacCutchan16-Dec-23 3:21

Richard MacCutchan

16-Dec-23 3:21

If you create an array with operator new as above, then you must tell delete that it is an array. So example 2 is the correct way to do it.

Re: C++ memory freeing

Mircea Neacsu16-Dec-23 3:21

Mircea Neacsu

16-Dec-23 3:21

Array delete operator, delete[] invokes the destructor of each array element before freeing the array. For an array of integers, it doesn't make any difference. Meanwhile, if the objects in the array have a non-trivial destructor you should call the delete[] operator.

Mircea

Re: C++ memory freeing

Daniel Pfeffer21-Dec-23 9:41

Daniel Pfeffer

21-Dec-23 9:41

Mircea Neacsu wrote:
For an array of integers, it doesn't make any difference.

It is true that no destructor is called for each element of an int[] array, but that does not mean that the memory layout is compatible with delete. For example, the compiler might allocate additional space for a variable containing the size of the array and return a pointer to memory after this variable. When using delete, the heap will be corrupted.

The heap layout is implementation-dependent, and therefore you should always match new/delete and new[]/delete[]!

Freedom is the freedom to say that two plus two make four. If that is granted, all else follows.
-- 6079 Smith W.

Re: C++ memory freeing

Mircea Neacsu21-Dec-23 15:26

Mircea Neacsu

21-Dec-23 15:26

While you are absolutely right, I don't know of any heap manager that behaves the way you describe. Let's say that calling delete on an int array is a smaller sin, a "peccadillo" that will place you on one of the first circles of hell. Laugh | :laugh:

Mircea

Re: C++ memory freeing

jschell18-Dec-23 5:30

jschell

18-Dec-23 5:30

As noted you should use the correct one.

I know for a fact that long ago using the wrong one would cause memory stack corruption.
I presume that now that isn't possible or is less likely.

Although I would be curious if the spec deals with that specific issue.

Re: C++ memory freeing

k505418-Dec-23 6:14

k5054

18-Dec-23 6:14

In any case, smart pointers are preferable in almost all cases to new/delete. I imagine that there are some cases where new and delete are preferred to smart pointers, but for most applications, a smart pointer is the better option.

"A little song, a little dance, a little seltzer down your pants"
Chuckles the clown

Finding the Parent Process

Richard Andrew x6415-Dec-23 8:21

Richard Andrew x64

15-Dec-23 8:21

I'm using NtQueryInformationProcess[^] to find the parent process of a specified process. I'm passing a PROCESS_BASIC_INFORMATION structure and using the InheritedFromUniqueProcessId member to get the parent.

I then call this function recursively with each parent process to find the parent of the parent, and so on.

The problem is that sometimes it starts returning process IDs that it has already returned in earlier calls, leading to infinite recursion.

For instance, in successive calls it will return process IDs 3, then 2, then 1. Then when called for process ID 1 it will return 3 again! How can this be?

I can easily work around this by checking to see if the returned parent process ID was already returned earlier in the call stack, and if it was, breaking out of the loop.

But my question is, why?

The difficult we do right away...
...the impossible takes slightly longer.

Re: Finding the Parent Process

Gerry Schmitz15-Dec-23 8:32

Gerry Schmitz

15-Dec-23 8:32

Dynamic versus static structures? Different types of parents / qualifying information?

"Before entering on an understanding, I have meditated for a long time, and have foreseen what might happen. It is not genius which reveals to me suddenly, secretly, what I have to say or to do in a circumstance unexpected by other people; it is reflection, it is meditation." - Napoleon I

Re: Finding the Parent Process

Richard Andrew x6415-Dec-23 8:47

Richard Andrew x64

15-Dec-23 8:47

Can you elaborate? I didn't know there were different types of parents. And I don't know what you mean by dynamic versus static structures.

The difficult we do right away...
...the impossible takes slightly longer.

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