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BRedding
Joined: 23 May 2022
Posts: 2
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| Using multidimensional string arrays |
 Posted: Mon May 23, 2022 4:57 am |
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I am trying to solve a problem of storing a menu in ROM and them using that to print to an LCD.
I have created a function:
print_lcd(char *str, int row, int col, ...)
This func works in the following code:
| Code: |
rom char single_string[22] = "This is a string";
print_lcd(single_string, 0, 0);
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but not in this code:
| Code: |
rom char multi_string[2][2][22] = {{"First string line",
"Second string line"},
{"Third string line",
"Final string line"}};
print_lcd(multi_string[0][0],0,0);
print_lcd(multi_string[0][1],1,0);
print_lcd(multi_string[1][0],2,0);
print_lcd(multi_string[1][1],3,0);
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It's not that the program won't compile, it just doesn't print anything to the lcd.
I assume I have made an enormous error in understanding of pics rather than this being hardware specific but I could be wrong so I'll include version numbers and everything:
PIC18F8722
Compiler ver 5.105 |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Mon May 23, 2022 5:42 am |
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I was able to make it work with the program below. It displays the
following output in the MPLAB vs. 8.92 Simulator's Sim Uart1 window:
| Quote: |
First string line
Second string line
Third string line
Final string line
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I compiled it with CCS vs. 5.108.
Test program:
| Code: |
#include <18F46K22.h>
#fuses NOWDT
#use delay(internal=4M)
#use rs232(UART1, baud=9600, ERRORS)
rom char multi_string[4][22] = "First string line",
"Second string line",
"Third string line",
"Final string line";
void print_lcd(rom char *str, int row, int col)
{
printf("%s\r", str);
}
//=======================================
void main()
{
print_lcd(&multi_string[0][0],0,0);
print_lcd(&multi_string[1][0],1,0);
print_lcd(&multi_string[2][0],2,0);
print_lcd(&multi_string[3][0],3,0);
while(TRUE);
}
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BRedding
Joined: 23 May 2022
Posts: 2
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| Posted: Mon May 23, 2022 7:01 am |
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Thank you PCM.
The & was the bit I was missing.
Could you please explain why that is needed in a const array of strings but not a single const string? |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19966
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| Posted: Tue May 24, 2022 1:16 am |
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& means 'the address of'.
Now the function being called requires an address. So '&'.
Key though is that in C, an array name "on it's own", is a shortcut for
it's address. So
multi_string equals &multi_string[0][0]
You can always use &, but the designers of C were trying to save you
from having to do this, when passing array addresses to functions.
However this 'hides' from you that when passing anything but the
whole array, you have got to remember to use &.... |
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