printf2.c

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/**
   @version 1.10 1997-07-01
   @author Cay Horstmann
*/

#include "Printf2.h"
#include <string.h>
#include <stdlib.h>
#include <float.h>

/**
   @param format a string containing a printf format specifier
   (such as "%8.2f"). Substrings "%%" are skipped.
   @return a pointer to the format specifier (skipping the '%')
   or NULL if there wasn't a unique format specifier
*/
char* find_format(const char format[])
{  
   char* p;
   char* q;

   p = strchr(format, '%');
   while (p != NULL && *(p + 1) == '%') /* skip %% */
      p = strchr(p + 2, '%');
   if (p == NULL) return NULL;
   /* now check that % is unique */
   p++;
   q = strchr(p, '%');
   while (q != NULL && *(q + 1) == '%') /* skip %% */
      q = strchr(q + 2, '%');
   if (q != NULL) return NULL; /* % not unique */
   q = p + strspn(p, " -0+#"); /* skip past flags */
   q += strspn(q, "0123456789"); /* skip past field width */
   if (*q == '.') { q++; q += strspn(q, "0123456789"); }
      /* skip past precision */
   if (strchr("eEfFgG", *q) == NULL) return NULL;
      /* not a floating point format */
   return p;
}

JNIEXPORT jstring JNICALL Java_Printf2_sprint(JNIEnv* env, jclass cl, 
   jstring format, jdouble x)
{  
   const char* cformat;
   char* fmt;
   jstring ret;

   cformat = (*env)->GetStringUTFChars(env, format, NULL);
   fmt = find_format(cformat);
   if (fmt == NULL)
      ret = format;
   else
   {  
      char* cret;
      int width = atoi(fmt);
      if (width == 0) width = DBL_DIG + 10;
      cret = (char*) malloc(strlen(cformat) + width);
      sprintf(cret, cformat, x);
      ret = (*env)->NewStringUTF(env, cret);
      free(cret);
   }
   (*env)->ReleaseStringUTFChars(env, format, cformat);
   return ret;
}