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Text resources and linker optimization

Sven Petersen

Hi there!

At present I am writing a program in C51 that might be available in different language versions one day. So I place all texts in one file called texts.h.

That file looks like
[...]

#define    OK_STR     "ok"
#define    CRLF_STR   "\x0D\x0a"

#define    MODEM_STR  "Modem"
[...]

Many of those strings are used several times in different C source files. Now my question... will those strings be located in one address in the code memory or will they be located once per module where they are used or will they be located for every time I use them?

I guess, I could make sure that a string only occures once in the code by creating constants in code space in a texts.c and make them public as global constants in texts.h. But that would be the harder way, since I have to type that string constant name at least three times (texts.c, texts.h and where I use them).

So, how does the linker optimize the string constants?

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  • 0

    Using a #define affects the output of the preprocessor. As far as the compiler in concerned, it just sees lots of literal strings with no immediately obvious connection between them.

    While it might theoretically be possible for an optimiser to pick up on the fact that one string is being used several times, I am pretty sure that C51 does not do this.

    Your best bet is to define constants stored in code memory, it is a little bit more trouble (but not much) and the program memory savings are potentially significant.

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  • 0

    Using a #define affects the output of the preprocessor. As far as the compiler in concerned, it just sees lots of literal strings with no immediately obvious connection between them.

    While it might theoretically be possible for an optimiser to pick up on the fact that one string is being used several times, I am pretty sure that C51 does not do this.

    Your best bet is to define constants stored in code memory, it is a little bit more trouble (but not much) and the program memory savings are potentially significant.

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