Support %n in scanf

  * Support `ftell` for memfile
  * Keep file caches if `fseek` is called for current position

Author: tyfkda

libsrc/stdio/_file.c

@@ -112,14 +112,17 @@ int _fflush(FILE *fp) {
   return 0;
 }
 
-int _fseek(void *cookie, off_t *offset, int origin) {
+int _fseek(void *cookie, off_t *poffset, int origin) {
   FILE *fp = cookie;
-  off_t result = lseek(fp->fd, *offset, origin);
+  off_t offset = *poffset;
+  off_t result = lseek(fp->fd, offset, origin);
   if (result == -1)
     return -1;
-  fp->flag &= ~FF_EOF;
-  fp->rp = fp->rs = 0;
-  fp->unget_char = EOF;
-  *offset = result;
+  if (offset != 0 || origin != SEEK_CUR) {
+    fp->flag &= ~FF_EOF;
+    fp->rp = fp->rs = 0;
+    fp->unget_char = EOF;
+  }
+  *poffset = result;
   return 0;
 }

libsrc/stdio/fmemopen.c

@@ -76,7 +76,12 @@ static int _memseek(void *cookie, off_t *offset, int origin) {
     fp->wp = fp->wcapa + *offset;
     break;
   }
-  fp->unget_char = EOF;
+  if (fp->unget_char != EOF) {
+    if (fp->wp > 0)
+      --fp->wp;
+    fp->unget_char = EOF;
+  }
+  *offset = 0;
   return 0;
 }
 

libsrc/stdio/ftell.c

@@ -1,9 +1,12 @@
 #include "stdio.h"
-#include "unistd.h"  // read
 
 #include "./_file.h"
 
 long ftell(FILE *fp) {
-  off_t result = lseek(fp->fd, 0, SEEK_CUR);
-  return result >= 0 ? result + fp->wp - (fp->rs - fp->rp) : result;
+  off_t o = 0;
+  ssize_t result = (fp->iof->seek)(fp, &o, SEEK_CUR);
+  if (result >= 0) {
+    result = o + fp->wp - (fp->rs - fp->rp);
+  }
+  return result;
 }

libsrc/stdio/vfscanf.c

@@ -206,7 +206,7 @@ int vfscanf(FILE *restrict fp, const char *restrict format, va_list ap) {
   VaList va;
   va_copy(va.ap, ap);
   for (const unsigned char *p = (unsigned char*)format; (c = *p) != '\0'; ++p) {
-    if ((c == '%' && p[1] != '%') || isspace(c)) {
+    if ((c == '%' && (p[1] != '%' && p[1] != 'n')) || isspace(c)) {
       int c2;
       while (c2 = fgetc(fp), isspace(c2))
         ;
@@ -271,6 +271,19 @@ int vfscanf(FILE *restrict fp, const char *restrict format, va_list ap) {
             continue;
           }
           break;
+        case 'n':
+          {
+            long pos = ftell(fp);
+            if (pos == -1) {
+              // error
+            } else {
+              int *p = va_arg(va.ap, int*);
+              *p = pos;
+              // No need to increment the `count`.
+              continue;
+            }
+          }
+          break;
         default:  // Unsupported.
           break;
         }

libsrc/tests/printf_test.c

@@ -45,12 +45,14 @@ TEST(fmemopen) {
   fp = fmemopen(buf, sizeof(buf), "w");
   if (EXPECT_NOT_NULL(fp)) {
     EXPECT_EQ(sizeof(str), fwrite(str, 1, sizeof(str), fp));
+    EXPECT_EQ(sizeof(str), ftell(fp));
     fclose(fp);
   }
 
   fp = fmemopen((void*)str, sizeof(str), "r");
   if (EXPECT_NOT_NULL(fp)) {
     EXPECT_EQ(sizeof(str), fread(buf, 1, sizeof(buf), fp));
+    EXPECT_EQ(sizeof(str), ftell(fp));
     fclose(fp);
     EXPECT_EQ(0, memcmp(buf, str, sizeof(str)));
   }

libsrc/tests/scanf_test.c

@@ -60,6 +60,12 @@ TEST(sscanf) {
     int result = sscanf("auto-whiltespaces: \t\n 333", "auto-whiltespaces:%d", &i);
     EXPECT_TRUE(result == 1 && i == 333);
   }
+
+  {
+    int i = -1, n = -1;
+    int result = sscanf("pos: 123  ", "pos: %d%n", &i, &n);
+    EXPECT_TRUE(result == 1 && i == 123 && n == 8);
+  }
 }
 
 XTEST_MAIN();