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@@ -1,9 +1,32 @@
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#include "stdio_impl.h"
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+/* Scan helper "stdio" functions for use by scanf-family and strto*-family
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+ * functions. These accept either a valid stdio FILE, or a minimal pseudo
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+ * FILE whose buffer pointers point into a null-terminated string. In the
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+ * latter case, the sh_fromstring macro should be used to setup the FILE;
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+ * the rest of the structure can be left uninitialized.
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+ *
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+ * To begin using these functions, shlim must first be called on the FILE
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+ * to set a field width limit, or 0 for no limit. For string pseudo-FILEs,
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+ * a nonzero limit is not valid and produces undefined behavior. After that,
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+ * shgetc, shunget, and shcnt are valid as long as no other stdio functions
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+ * are called on the stream.
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+ *
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+ * When used with a real FILE object, shunget has only one byte of pushback
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+ * available. Further shunget (up to a limit of the stdio UNGET buffer size)
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+ * will adjust the position but will not restore the data to be read again.
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+ * This functionality is needed for the wcsto*-family functions, where it's
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+ * okay because the FILE will be discarded immediately anyway. When used
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+ * with string pseudo-FILEs, shunget has unlimited pushback, back to the
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+ * beginning of the string. */
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+
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hidden void __shlim(FILE *, off_t);
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hidden int __shgetc(FILE *);
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-#define shcnt(f) ((f)->shcnt + ((f)->rpos - (f)->rend))
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+#define shcnt(f) ((f)->shcnt + ((f)->rpos - (f)->buf))
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#define shlim(f, lim) __shlim((f), (lim))
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-#define shgetc(f) (((f)->rpos < (f)->shend) ? *(f)->rpos++ : __shgetc(f))
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+#define shgetc(f) (((f)->rpos != (f)->shend) ? *(f)->rpos++ : __shgetc(f))
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#define shunget(f) ((f)->shend ? (void)(f)->rpos-- : (void)0)
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+
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+#define sh_fromstring(f, s) \
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+ ((f)->buf = (f)->rpos = (void *)(s), (f)->rend = (void*)-1)
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