C / C++ / MFC

28-Jul-07 18:56

hi guys.
i have a simple problem but can't seem to find the solution anywhere..

background:
i have a double and an array of char*. i used reinterpret_cast to convert the double into a char* and then stored it in a particular index. now given that, i want to add a null character, '\0', at the end of that char* that stores the double.

relevant code:
char* results_text[7];
results_text[0] = reinterpret_cast<char*>(static_cast<int>(m->total_time_taken));

how should i got about doing this? i am flexible in changing the method as long as the end result meets the following conditions: it is a char* holding the double value + a null character at the end.

thanks in advance.

--
dg

cp987628-Jul-07 22:18

28-Jul-07 22:18

Why don't you just post your code to the Coding Horrors forum and be done with it!

Forget the code you have written, what are you trying to achieve?

Peter
"Until the invention of the computer, the machine gun was the device that enabled humans to make the most mistakes in the smallest amount of time."

moonraker92828-Jul-07 22:26

28-Jul-07 22:26

I am using GLUT to print out a char* to my window much like this:

renderBitmapString(45, window_height-90, 0.0, GLUT_BITMAP_HELVETICA_18, "testing...");

this function takes the char* and loops through it until the '/0' is seen and one-by-one uses the glutBitmapCharacter(void* font, int char) to print out the characters...

now if i cast a double into a char*, the '/0' is missing at the end so it results in a infinite loop and a runtime error...

i have tried to find a glut function that can print double to the screen but haven't succeeded. if you know an alternative way to do this or a solution to this problem, i would appreciate it very much!

thanks!

--
dg

cp987628-Jul-07 22:49

28-Jul-07 22:49

an MFC solution:

<br />
double d = 1.234;<br />
CString str;<br />
str.Format("%f", d);<br />
renderBitmapString(45, window_height-90, 0.0, GLUT_BITMAP_HELVETICA_18, str);<br />

You can control the formatting of the double in the Format call. If you are not using MFC, look at sprintf, or there is probably a way of doing it with the STL string class.

Peter
"Until the invention of the computer, the machine gun was the device that enabled humans to make the most mistakes in the smallest amount of time."

moonraker92828-Jul-07 22:59

28-Jul-07 22:59

I used sprintf...here is the code:

sprintf(results_text[0],"%f",3.14);
renderBitmapString(205, window_height-90, 0.0, GLUT_BITMAP_HELVETICA_18, results_text[0]);

[ NO COMPILER ERRORS ]

However, during runtime, I get popup window saying:

Debug Assertion Failed!
Program:...
File: sprintf.c
Line: 110

..I'm lost..

--
dg

cp987628-Jul-07 23:45

28-Jul-07 23:45

Did you allocate any memory for results_text[0]? If not sprintf will try to write to wherever the uninitialised pointer results_text[0] points to.

Peter
"Until the invention of the computer, the machine gun was the device that enabled humans to make the most mistakes in the smallest amount of time."

moonraker92829-Jul-07 10:08

29-Jul-07 10:08

This line allocates memory and was included when I was running the application:
char* results_text[7];

am i right? or are you talking about something else..

--
dg

cp987629-Jul-07 12:59

29-Jul-07 12:59

moonraker928 wrote:
char* results_text[7];

allocates an array of 7 character pointers. If you are trying to allocate a buffer for characters:

<br />
double d = 3.14;<br />
char text[128];<br />
sprintf(text, "%f", d);<br />

Be careful with sprintf() that you don't overwrite the buffer - there is a safer version in VS20058 - sprintf_s(). Making the buffer only 7 characters long needs care, I've allocated 128 bytes to be safe.

Peter
"Until the invention of the computer, the machine gun was the device that enabled humans to make the most mistakes in the smallest amount of time."

moonraker92829-Jul-07 13:03

29-Jul-07 13:03

ok i solved the problem - i had to initialize the char as char str[10] instead of char* str.

what a silly reason ... for wasting all that time..

--
dg

cp987629-Jul-07 13:36

29-Jul-07 13:36

If you are allocating such a short array you either have to be very careful that sprintf does not write past the end of the array (remembering the null terminator) or use the safe version. If sprintf writes past the end of the buffer you will get bugs that can be very hard to track down.

I can't find the limit of width using %f, but a quick test with printf("Pi = %f", 1000000000000*pi) gives "Pi = 3141592653589.793000" showing that the %f specifier can print 20 characters at least. So printing using %f to a buffer of length 10 using sprintf is dangerous at best.

Peter
"Until the invention of the computer, the machine gun was the device that enabled humans to make the most mistakes in the smallest amount of time."

User 58385229-Jul-07 18:34

User 583852

29-Jul-07 18:34

10 points for patience!

cp987629-Jul-07 19:08

29-Jul-07 19:08

Peter
"Until the invention of the computer, the machine gun was the device that enabled humans to make the most mistakes in the smallest amount of time."

David Crow30-Jul-07 4:12

David Crow

30-Jul-07 4:12

You need to allocate memory first:

results_text[0] = new char[6];
sprintf(...);

"A good athlete is the result of a good and worthy opponent." - David Crow

"To have a respect for ourselves guides our morals; to have deference for others governs our manners." - Laurence Sterne

Mark Salsbery30-Jul-07 6:43

Mark Salsbery

30-Jul-07 6:43

moonraker928 wrote:
i have a double and an array of char*. i used reinterpret_cast to convert the double into a char* and then stored it in a particular index.

Ouch.

If there was a programmer penalty box, you would be sent to it, and not allowed to use
reinterpret_cast for 2 months Poke tongue | ;-P

Mark

Mark Salsbery
Microsoft MVP - Visual C++
Java | [Coffee]

moonraker92830-Jul-07 9:18