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SamMeredith
Joined: 13 Jul 2018
Posts: 23
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| [Solved] Passing const string arrays |
 Posted: Fri Jul 13, 2018 5:32 am |
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Compiler V5.068
PIC 33EP512MC806
I am trying to write a function which prints an array of strings from ROM, but in contrast to similar questions I have read on this issue, I want to pass the string array as a parameter.
I get something like this
| Code: |
const char MAIN_TEXT[][TEXT_LENGTH] = {
"Main Menu",
" (1) Thing 1",
" (2) Thing 2"
};
const char THING1_TEXT[][TEXT_LENGTH] = {
"Thing 1 Menu",
....
};
void print_menu(rom char *menu_text) {
char buffer[TEXT_LENGTH];
sprintf(buffer, "%s", menu_text);
while( strlen(buffer) > 0) {
fprintf(OUTPUT_STREAM, buffer);
menu_text += TEXT_LENGTH;
sprintf(buffer, "%s", menu_text);
}
}
void main() {
....
print_menu(MAIN_TEXT);
....
}
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But the result of this is menu_text only contains the first string from whichever array is passed. This seems to make sense given what I have read: a copy of the string from ROM is being created in RAM as needed, and since passing MAIN_TEXT is treated as if I had passed &MAIN_TEXT[0] I only get the first string.
I have tried instead passing a pointer to MAIN_TEXT and correspondingly modifying my print function, but to no success.
How might I go about solving this?
Last edited by SamMeredith on Fri Jul 13, 2018 7:33 am; edited 1 time in total |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19546
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| Posted: Fri Jul 13, 2018 7:12 am |
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There are several separate problems...
First strlen, does not support operation with a rom pointer.
Then you need to declare the array as 'rom', rather than const, to allow the pointer to be constructed.
Then your array needs to contain a zero length final string for the exit condition to be met.
| Code: |
#define TEXT_LENGTH 14
rom char MAIN_TEXT[][TEXT_LENGTH] = {
"Main Menu",
" (1) Thing 1",
" (2) Thing 2",
"" //to give a zero length final string
};
#include <stdlib.h>
#include <string.h>
void print_menu(rom char *menu_text) {
char buffer[TEXT_LENGTH];
while (*menu_text != '\0') {
fprintf(OUTPUT_STREAM, "%s\n",menu_text);
menu_text += TEXT_LENGTH;
}
}
void main()
{
print_menu(MAIN_TEXT);
while(TRUE)
{
delay_cycles(1);
}
}
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This shows how to handle such a table.  |
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SamMeredith
Joined: 13 Jul 2018
Posts: 23
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| Posted: Fri Jul 13, 2018 7:32 am |
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Wow, just like that!
Thank you very much, that has solved my problem. |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19546
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| Posted: Fri Jul 13, 2018 7:46 am |
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| Using pointers to ROM is a little bit of a 'black art', I've been one of the people who has played with it from when they were first introduced, and have met most of the issues at one time or another!... |
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