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POA reader interface that consumes FILEs and char* in C
 

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  1. POA reader interface that consumes FILEs and char* in C
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    <p>I am modifying a parser I've inherited which currently only reads from FILE* via read. It now has the requirement of being able to pull data from char* constants as well so inline text inside C strings can be parsed.</p> <p>I've looked at providing a simple interface to both in the form of "readers" so you can provide a file reader and a char reader from which the parser can grab characters. For example:</p> <pre><code>// Inputs const char *str = "stringToParse"; FILE *f = fopen(...); // Creating a reader. Each reader stores a function ptr to a destructor // which closes the file if required and an internal state object. Reader *r = FileReader(f); // -or- Reader *r = CharReader(str); // Start parsing --------------------------- // Inside the parser, repeated calls to: int error = ReadBytes(&amp;buf /* target buf */, &amp;nRead /* n read out */, maxBytes /* max to read */); // End parsing ----------------------------- CloseReader(&amp;r); // calls destructor, free's state, self </code></pre> <p>I'd like to keep this really simple. Are there any obvious other ways to achieve this using less infrastructure that I have missed? </p> <p>Note: I have simplified this considerably from what is there to highlight the programming interface concerns. It actually uses wchar_t internally and a mush of encoding stuff and is a bit of a rat's nest which I will untangle at the same time.</p> <hr> <p>Thanks to everyone who answered. The cleanest answer is to use fmemopen. I've provided a full example below:</p> <pre><code>#include &lt;stdio.h&gt; #include &lt;string.h&gt; void dump(FILE *f) { char c; while ((c = fgetc(f)) != EOF) putchar(c); } int main(int argc, char *argv[]) { /* open string */ const char str[] = "Hello string!\n"; FILE *fstr = fmemopen(&amp;str, strlen(str), "r"); /* open file */ FILE *ffile = fopen("hello.file", "r"); /* dump each to stdout */ dump(ffile); dump(fstr); /* clean up */ fclose(ffile); fclose(fstr); } </code></pre>
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