Difference between revisions of "Multi language C embedded"

Revision as of 16:40, 27 May 2018

Different approaches of implementing multi language support in embedded C projects. (See links below).

Design goals

Should only exist in flash. (No copying to RAM)
Logical for translators to translate from english to other language.
Easy to change language on-the-fly
No padding of strings to max length in arrays
- In the example below the text strings yes and no use the same amount of memory as the long message and will be copied to RAM on a system with firmware.

char txt[3][] = {
  "Yes",
  "No",
  "The format received is inconsistent with RFC 1024",
};

Simple Example

In this small example both languages are in the same file. In a project, you should have a file called english.h where all your english messages should reside. When the project is internationalized send a copy of english.h to the translator with a new name. For example german.h

Remember: The translator must keep the variables as indicated by %<TYPE> in all messages.

char const * const danish[] = {
  "FEJL: Kommando eksisterer ikke: %s",
  "FEJL: Dato %s ugyldig",
  "Advarsel: Der er kun %u%% batteri tilbage!"
};
char const * const english[] = {
  "ERROR: Non-existing command: %s",
  "ERROR: Invalid Date %s",
  "Warning: Only %u%% battery left!"
};
void example(void) {
  char **textmes;
  
  textmes = (char **) &danish;  // Set danish language
  printf( textmes[2], 17);      // Outputs: Advarsel: Der er kun 17% batteri tilbage!
  textmes = (char **) &english; // Set english language
  printf( textmes[2], 17);      // Outputs: Warning: Only 17% battery left!

}

The drawback of this method is that the array-members need to come in this exact order and if you delete one of the members, it’s necessary to leave an empty (“”) string as the array-member number is the reference to the string when used. For example textmes(2) references the battery warning.

Using array initialization with enum indices

It is possible to initialize arrays – even const arrays – referencing members at compiletime.

enum Errors {
     ERR_NONEXCOM = 0,
     ERR_INVDATE,
     ERR_LOWBAT,
 } err;

char const * const danish[] = {
    [ERR_NONEXCOM]  = "FEJL: Kommando eksisterer ikke: %s",
    [ERR_INVDATE]   = "FEJL: Dato %s ugyldig",
    [ERR_LOWBAT]    = "Advarsel: Der er kun %u%% batteri tilbage!"
 };

char const * const english[] = {
    [ERR_NONEXCOM]  = "ERROR: Non-existing command: %s",
    [ERR_INVDATE]   = "ERROR: Invalid Date %s",
    [ERR_LOWBAT]    = "Warning: Only %u%% battery left!"
};

void example(void) {
  char **textmes;
        int i;
 
      textmes = (char **) &english; // Set english language
      printf( textmes[ERR_LOWBAT], 17);      // Outputs: Warning: Only 17% battery left!
      textmes = (char **) &danish;  // Set danish language
      printf( textmes[ERR_LOWBAT], 17);      // Outputs: Advarsel: Der er kun 17% batteri tilbage!
}