<div dir="ltr"><br><div class="gmail_extra"><br><br><div class="gmail_quote">On Mon, Oct 14, 2013 at 2:34 PM, William Moses <span dir="ltr"><<a href="mailto:moses.williamsteven@gmail.com" target="_blank">moses.williamsteven@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">However, how would one allocate the buffer for a string if you did not know the length of the string at compile time?<br>
</div></blockquote><div><br></div><div>FYI, LLVM doesn't provide a "platform" or "VM" or "runtime". You will need to be familiar with your target platform's API's; on most platforms you can probably get away with just calling malloc for the case at hand though.</div>
<div><br></div><div>-- Sean Silva</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><br>For instance, using the api how would one reproduce the code for the following c++ function?<br>
<br>std::string add(std::string a, std::string b){<br> return a+b;<br>}<br><br>When allocating the buffer required for the new string, one can determine the length at runtime, however I do not know how one can allocate a global array with its size determined by a Value*.
<div><div class="h5"><div class="gmail_extra"><br><br><div class="gmail_quote">On Mon, Oct 14, 2013 at 5:46 AM, Jeremy Lakeman <span dir="ltr"><<a href="mailto:Jeremy.Lakeman@gmail.com" target="_blank">Jeremy.Lakeman@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><div><div><div>The toy language I've been playing around with represents all strings as a struct in llvm;<br>
</div><br>struct string{<br></div> char *ptr;<br></div> int str_len;<br></div> int buffer_len;<br>
<div><div><div><div>}<br><br></div><div>And my AST has an interface like;<br><br></div><div>String_AST{<br></div> int measure();<br><div> void copy(char *dest);<br><div> struct string get_value();<br>}<br><br></div><div>
A constant string can be measured at compile time, for a string variable measure() just extracts str_len. Strings passed in from other external sources are measured immediately, but llvm optimisations will eliminate the call if the return value isn't used.<br>
<br>The implementation of get_value() for a concatenation AST node can generate code to evaluate each sub string, measure them, allocate the final buffer length, and only then copy each sub string directly into the final buffer.<br>
<br>I also support a string append operation that will reallocate the buffer only if the existing one is too small.<br></div><br></div><div>Ultimately you will need to work out if you want pascal / java style strings like mine, or C style NULL terminated strings. And how the memory for these strings will be managed.<br>
</div></div></div></div></div><div class="gmail_extra"><br><br><div class="gmail_quote"><div><div>On Sun, Oct 13, 2013 at 4:43 AM, William Moses <span dir="ltr"><<a href="mailto:moses.williamsteven@gmail.com" target="_blank">moses.williamsteven@gmail.com</a>></span> wrote:<br>
</div></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div><div dir="ltr">All,<br><br>I am building my own language with llvm as the base.<br><br>
I was working on string concatenation (where a string is just an array of characters cast to a pointer to a character (i8*) ). Given two strings, it is possible to determine the length of new string by summing the number of characters until the null terminator and adding one.<br>
<br>Unfortunately, I have no idea how to use the c-api to store this. As the length of the new string is not a compile-time constant (e.g. stored in a Value*), I cannot determine at compile-time what length the llvm array-type will be? Therefore, I cannot create the GlobalVariable since I do not know the type.<br>
<br>One possible solution I thought of was linking to the malloc function and calling that, but I'm sure there's a better way. If any of you have implemented a similar sort of string concatenation, I would much appreciate any advice that you could give.<br>
<br>Thanks,<br>Billy</div>
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