C / C++ / MFC

const char [] and char[] difference question

11-May-18 6:34

Thanks Richard, you are a pal.
Appreciate your comments.

focusdoit10-May-18 14:26

focusdoit

10-May-18 14:26

Hi, I wrote a small c program on a microcontroller, 32bit.

I met a weird problem.

I wrote code like:

C++

const char strtest[] = "Test123\r\n"; //Global
UART_print(strtest); //in a loop

the output is fine, I can see the output on Teraterm(RS232 interface tool), like:
Test123
Test123
..

But when I try code:

char str123[] = "Test123\r\n";  //Global
UART_print(strtest); //in a loop

The output is only the first element:
TTTTTTTT

Any hint is appreciated.

David Crow10-May-18 17:22

David Crow

10-May-18 17:22

focusdoit wrote:
char str123[] = "Test123\r\n"; //Global
UART_print(strtest); //in a loop

Where is str123 used?

What is the signature of UART_print()?

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Richard MacCutchan10-May-18 21:25

10-May-18 21:25

Please show the code for the UART_print function.

Victor Nijegorodov10-May-18 23:03

Victor Nijegorodov

10-May-18 23:03

focusdoit wrote:

But when I try code:

char str123[] = "Test123\r\n";  //Global
UART_print(strtest); //in a loop

You defined the variable str123 but you print the strtest. Where and how is this strtest defined?

Please advise me on C++ coding structure

samzcs11-May-18 2:24

samzcs

11-May-18 2:24

It's memory allocation problem. the MCU has 2 cpu inside, and one set of peripheral units, compiler put str123 in DMA Access prohibited area.

Embedded programming, too many tricks.

Smile | :)

Vaclav_9-May-18 4:24

Re: Please advise me on C++ coding structure

9-May-18 4:24

I like to rebuild my Raspberry Pi code to have "top down" structure.
On top would be the device "primitives" class - for example LCD draw circle
In middle I like to have hardware specifics, maybe even protocol (SPI,I2C) specifics - BCMx processor
And finally the access to I/O "pins"

I was thinking of "cascaded C++ " hierarchy but it would not be C++ hierarchy for real.
Or just simple top class having supporting class as variable. Not sure how flexible that would be.

The idea is to be able to add another "top" device and reuse the supporting classes.
I hope this makes sense and if I have asked this before - just ignore OF.

Thanks
Cheers Vaclav

leon de boer9-May-18 4:44

leon de boer

9-May-18 4:44

It actually more complex than that because on a Pi2,Pi3 you have 4 cores so you will have spinlocks/semaphores on all the devices.

What are you doing with cores 1,2,3 at the moment are they still parked or in use?
I assume your code isn't under linux given you have dragged the devices out to objects Smile | :)

Assuming baremetal I would strongly suggest you look at circle
GitHub - rsta2/circle: A C++ bare metal environment for Raspberry Pi with USB[^]

I am not sure you can develop much of a hierarchy it all needs to be fairly flat if you want to use the multicores, welcome to multicore programming Smile | :)

In vino veritas

modified 9-May-18 11:28am.

Help with C

Faith Burnett5-May-18 10:28

Faith Burnett

5-May-18 10:28

I have been taking the free CS50x course from Harvard and just completed the Mario more comfortable problem. This is my code and I wanted to know how the right side of hashes are left aligned even though the code is the same for both left and right hashes.? To be honest I’m new to this and thought it would simply print out two right aligned pyramids with a gap in between.
// Prints bricks, sized as specified by user

#include <cs50.h>
#include <stdio.h>

int main(void)
{
// Prompt user for a positive number to use as height of pyramid
int h;
do
{
h = get_int("Height: ");
}
while (h < 0 || h > 23);

// Print out this many rows
for (int i = 0; i < h; i++)
{
// Print out this many spaces
for (int j = 0; j < h - i; j++)
{
printf(" ");
}
// Print left hashes
for (int j = 0; j < i + 2; j++)

{
printf("#");
}
// Print gap
printf(" ");

// Print right hashes
for (int j = 0; j < i + 2; j++)
{
printf("#");
}
printf("\n");
}
}

Re: Help with C

David Crow5-May-18 16:57

David Crow

5-May-18 16:57

Faith Burnett wrote:
To be honest I’m new to this and thought it would simply print out two right aligned pyramids with a gap in between.

Those two for() loops are printing the same NUMBER of hashes from where the stdout stream happens to be at the point the for() loop starts printing. Since the stdout stream is at "column" 0 before the first for() loop, the first set of hashes is right justified (preceded with spaces), and since the stdout stream is at "column" H+2 after the first two inner for() loops run, the second set of hashes always starts in the same "column."

You might want to consider changing your for() loop boundaries so that the pyramid has a "pointed" top at level 1, and no leading/trailing spaces at level h:

for (int i = 0; i < h; i++)
{
    ...
    // Print out this many spaces
    for (int j = 0; j < h - i - 1; j++)
    ...
    // Print left hashes
    for (int j = 0; j < i + 1; j++)
    ...
    // Print right hashes
    for (int j = 0; j < i + 1; j++)
    ...
}

modified 6-May-18 0:28am.

Re: Help with C

Faith Burnett5-May-18 19:08

Faith Burnett

5-May-18 19:08

Thanks for the help David!

How to get value

Vaclav_5-May-18 4:41

5-May-18 4:41

I like to verify actuall value passed from char array to struct pointer

buf array declaration
unsigned char buf[32]; // = { 0x00, 0x04 };
value passed unsigned char 0x04;
buf[0] = command; // passed 0x04 software reset
transmit buffer assignment
xfer[0].tx_buf = (unsigned long) buf;

Now I like to use cout to print the actual value in tx_buf.
From struct declaration I know "tx_buf" is a unsigned long pointer.

Not sure how to access the required value
this gives me the pointer as expected:

<pre lang="c++">cout << "xfer[0].tx_buf " << xfer[0].tx_buf<< endl;

Once I know how to get first value I can probably figure out how to get the whole buf[32] array values.

Thanks for help
Cheers Vaclav

Richard MacCutchan5-May-18 5:47

5-May-18 5:47

You need to print each byte independently, after casting them to int, since the char values are unprintable. Something like:

C++

cout << hex << (int)buf[0] << endl;

Use a loop to print more than one value.

Vaclav_6-May-18 3:54

6-May-18 3:54

Thanks, but...
I know how to get buf values, what I wanted to verify is that the buf values are actually passed to the struct.

I am having issues verifying that the struct has all of the necessary data.
Some are "straight" values, most via pointers.

BTW
When I use "modifier" hex , not sure I am using correct term as always, in cout << hex << (int)buf[0] << endl;,

then following usage WITHOUT such modifier will continue to print the data in hex
cout << int)buf[0] << endl;

Nice but it can get out of control.

Richard MacCutchan6-May-18 4:48

6-May-18 4:48

Vaclav_ wrote:
I am having issues verifying that the struct has all of the necessary data.

You need to be specific, we cannot guess what these issues may be. And, TBH, my previous reply was also based on a bit of guesswork.

See <iomanip> functions[^] for details on using the hex manipulator.

Vaclav_6-May-18 6:49

6-May-18 6:49

I just like <b>to see the value</b> passed to struct pointer.
I can deal with what the functio0n does with it myself.
Perhaps it is all working correctly and my problems are elsewhere.

Wrapping c++

Member 129991324-May-18 22:48

Member 12999132

4-May-18 22:48

I am trying to wrap a c++ class for c. The function uses pass by reference.
Example
Test::funcref(int & h,BSTR & b)

void wrap_funcref(wrap_t *m, int h, BSTR)
{
Test *obj;

if (m == NULL)
return;

obj = static_cast<test *="">(m->obj);
obj->funcref(&h,&b);
}

Not sure if I need to change the c++ functions for *

Re: Wrapping c++

Richard MacCutchan5-May-18 1:26

5-May-18 1:26

C++

obj = static_cast<Test *>(m->obj); // static_cast is C++ not C
obj->funcref(&h,&b);  // The C compiler may not generate what you expect here
}

How do you define Test and wrap_t in your C code?

Re: Wrapping c++

Member 129991325-May-18 5:06

Member 12999132

5-May-18 5:06

Hi richard thanks for the reply
obj->funcref(&h,&b); I know this wont work, don't know why I even typed it.
Any way here goes

file.cpp

//------------
// CONSTRUCTOR
//------------
Test::Test()
{
}

//-----------
// DESTRUCTOR
//-----------
Test::~Test()
{
}

HRESULT Test::funcref(int &h, BSTR &b )
{
HRESULT hr = S_OK
char cstr[200];
strcpy_s(cstr, "BLAHHHHH");
*b = A2BSTR(cstr);
return hr;
}

HRESULT Test::funcp(int i,int *y)
{
HRESULT hr = S_OK
*y = i +7;
return hr;
}

file.h
class Test
{
public:
Test();
virtual ~Test();

static HRESULT funcref( int &h,BSTR &b);
static HRESULT funcp(int i, int *y);

};

wrapit.cpp

struct wrapStruct
{
void *obj;

};

extern "C" __declspec(dllexport) wrap_t *wrap_create()
{
wrap_t *m;
Test*obj;

m = static_cast(malloc(sizeof(*m)));

obj= new Test();
m->obj = obj;

return t;
}
extern "C" __declspec(dllexport) void wrap_destroy(wrap_t *m)
{

if (m == NULL)
return;
delete static_cast(m->obj);
free(m);
}

extern "C" __declspec(dllexport) int wrap_funcp(wrapper_L2H *m,int i,int* y)
{
Test *obj;
if (m == NULL)
return false;
obj= static_cast(m->obj);
obj->funcp(i, y);
return true;
}

extern "C" wrapper_API void wrap_funcref(wrap_t *m, int* h,BSTR* b) //?
{
Test *obj;
if (m == NULL)
return false;
obj = static_cast(m->obj);
obj->funcref(h, b);
return true;
}

wrapit.h

#ifdef WRAPPER_EXPORTS
#define wrapper_API __declspec(dllexport)
#else
#define wrapper_API __declspec(dllimport)
#endif

struct wrapStruct;

typedef struct wrapStruct wrap_t

extern "C" wrapper_API wrap_t* wrap__create();

extern "C" wrapper_API void wrap__destroy(wrap_t *m);

extern "C" wrapper_API void wrap_funcref(wrap_t *m, int *h, BSTR* b); //?
extern "C" wrapper_API void wrap_funcp(wrap_t *m, int *y;

useit.c

#include "wrapit.h"

int z=0,uu=0,d=0,p=0;

BSTR uu,nn;
wrap_t *z = wrap_create();

wrap_funcref(&p,&nn); //not sure does not work
wrap_funcp(z,&uu); //works

wrap_destroy(z);

wrap_funcp works
wrap_funcref does not.

Re: Wrapping c++

Richard MacCutchan5-May-18 5:42

Re: help: list<struct> of list<string>

5-May-18 5:42

C++

wrap_funcref(&p,&nn);	//not sure does not work

Where is p defined, and what is it? And where is the missing parameter that should be included per the declaration:

C++

extern "C" wrapper_API void wrap_funcref(wrap_t *m, int *h, BSTR* b); //?

Some of this might also make a bit more sense if it was properly formatted between <pre lang="c++"></pre> tags, as my samples above. And the use of single letters for variable names is confusing.

Message Closed

2-May-18 23:33

Lapmangfpt

2-May-18 23:33

Message Closed

-- modified 20-Jun-18 4:35am.

Victor Nijegorodov2-May-18 23:57

Victor Nijegorodov

2-May-18 23:57

Lapmangfpt wrote:
j = find(MyList[i].key.begin(), MyList[i].key.end(), tkey); // ERROR 1
// If not, add key and content
if (j == -1) // ERROR 2

You have to compare not wit -1, but with MyList[i].key.end()

The Breakpoint will not be hit the Source Code is different then the orignal

ForNow30-Apr-18 16:08

ForNow

30-Apr-18 16:08

Hi

I have gotten this error from time to time but have always gotten around by doing a build or rebuild
this time I even tried a clean nothing helps

Just wondering is the source stored in the PDB file

Re: The Breakpoint will not be hit the Source Code is different then the orignal

Richard MacCutchan30-Apr-18 21:32