[libexif-cvs] libexif/contrib/examples write-exif.c,1.2,1.3

[Dan F. <dfa...@us...>]

Update of /cvsroot/libexif/libexif/contrib/examples
In directory sfp-cvsdas-2.v30.ch3.sourceforge.com:/tmp/cvs-serv27395/contrib/examples

Modified Files:
	write-exif.c 
Log Message:
Fixed some memory leaks in the write-exif.c example program and
added some examples of allocating a new tag.                   


Index: write-exif.c
===================================================================
RCS file: /cvsroot/libexif/libexif/contrib/examples/write-exif.c,v
retrieving revision 1.2
retrieving revision 1.3
diff -u -p -d -r1.2 -r1.3
--- write-exif.c	17 Jun 2009 19:07:45 -0000	1.2
+++ write-exif.c	9 Dec 2009 06:17:19 -0000	1.3
@@ -13,6 +13,8 @@
  */
 
 #include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
 #include <assert.h>
 #include <libexif/exif-data.h>
 
@@ -114,21 +116,83 @@ static const unsigned char exif_header[]
 static const unsigned int exif_header_len = sizeof(exif_header);
 
 /* byte order to use in the EXIF block */
-#define BYTE_ORDER EXIF_BYTE_ORDER_INTEL
+#define FILE_BYTE_ORDER EXIF_BYTE_ORDER_INTEL
+
+/* comment to write into the EXIF block */
+#define FILE_COMMENT "libexif demonstration image"
+
+/* special header required for EXIF_TAG_USER_COMMENT */
+#define ASCII_COMMENT "ASCII\0\0\0"
+
 
 /* Get an existing tag, or create one if it doesn't exist */
 static ExifEntry *init_tag(ExifData *exif, ExifIfd ifd, ExifTag tag)
 {
 	ExifEntry *entry;
+	/* Return an existing tag if one exists */
 	if (!((entry = exif_content_get_entry (exif->ifd[ifd], tag)))) {
+	    /* Allocate a new entry */
 	    entry = exif_entry_new ();
 	    assert(entry != NULL); /* catch an out of memory condition */
+	    entry->tag = tag; /* tag must be set before calling
+				 exif_content_add_entry */
+
+	    /* Attach the ExifEntry to an IFD */
 	    exif_content_add_entry (exif->ifd[ifd], entry);
+
+	    /* Allocate memory for the entry and fill with default data */
 	    exif_entry_initialize (entry, tag);
+
+	    /* Ownership of the ExifEntry has now been passed to the IFD.
+	     * One must be very careful in accessing a structure after
+	     * unref'ing it; in this case, we know "entry" won't be freed
+	     * because the reference count was bumped when it was added to
+	     * the IFD.
+	     */
+	    exif_entry_unref(entry);
 	}
 	return entry;
 }
 
+/* Create a brand-new tag with a data field of the given length, in the
+ * given IFD. This is needed when exif_entry_initialize() isn't able to create
+ * this type of tag itself, or the default data length it creates isn't the
+ * correct length.
+ */
+static ExifEntry *create_tag(ExifData *exif, ExifIfd ifd, ExifTag tag, size_t len)
+{
+	void *buf;
+	ExifEntry *entry;
+	
+	/* Create a memory allocator to manage this ExifEntry */
+	ExifMem *mem = exif_mem_new_default();
+	assert(mem != NULL); /* catch an out of memory condition */
+
+	/* Create a new ExifEntry using our allocator */
+	entry = exif_entry_new_mem (mem);
+	assert(entry != NULL);
+
+	/* Allocate memory to use for holding the tag data */
+	buf = exif_mem_alloc(mem, len);
+	assert(buf != NULL);
+
+	/* Fill in the entry */
+	entry->data = buf;
+	entry->size = len;
+	entry->tag = tag;
+	entry->components = len;
+	entry->format = EXIF_FORMAT_UNDEFINED;
+
+	/* Attach the ExifEntry to an IFD */
+	exif_content_add_entry (exif->ifd[ifd], entry);
+
+	/* The ExifMem and ExifEntry are now owned elsewhere */
+	exif_mem_unref(mem);
+	exif_entry_unref(entry);
+
+	return entry;
+}
+
 int main(int argc, char **argv)
 {
 	int rc = 1;
@@ -145,7 +209,7 @@ int main(int argc, char **argv)
 	/* Set the image options */
 	exif_data_set_option(exif, EXIF_DATA_OPTION_FOLLOW_SPECIFICATION);
 	exif_data_set_data_type(exif, EXIF_DATA_TYPE_COMPRESSED);
-	exif_data_set_byte_order(exif, BYTE_ORDER);
+	exif_data_set_byte_order(exif, FILE_BYTE_ORDER);
 
 	/* Create the mandatory EXIF fields with default data */
 	exif_data_fix(exif);
@@ -153,22 +217,41 @@ int main(int argc, char **argv)
 	/* All these tags are created with default values by exif_data_fix() */
 	/* Change the data to the correct values for this image. */
 	entry = init_tag(exif, EXIF_IFD_EXIF, EXIF_TAG_PIXEL_X_DIMENSION);
-	exif_set_long(entry->data, BYTE_ORDER, image_jpg_x);
+	exif_set_long(entry->data, FILE_BYTE_ORDER, image_jpg_x);
 
 	entry = init_tag(exif, EXIF_IFD_EXIF, EXIF_TAG_PIXEL_Y_DIMENSION);
-	exif_set_long(entry->data, BYTE_ORDER, image_jpg_y);
+	exif_set_long(entry->data, FILE_BYTE_ORDER, image_jpg_y);
 
 	entry = init_tag(exif, EXIF_IFD_EXIF, EXIF_TAG_COLOR_SPACE);
-	exif_set_short(entry->data, BYTE_ORDER, 1);
+	exif_set_short(entry->data, FILE_BYTE_ORDER, 1);
 
-	/* A good example to give here would be to add a new tag that isn't
-	 * automatically created by exif_data_fix() (such as
-	 * EXIF_TAG_USER_COMMENT) which requires allocating memory in
-	 * entry->data. This isn't so easy to do, unfortunately.
+	/* Create a EXIF_TAG_USER_COMMENT tag. This one must be handled
+	 * differently because that tag isn't automatically created and
+	 * allocated by exif_data_fix(), nor can it be created using
+	 * exif_entry_initialize() so it must be explicitly allocated here.
 	 */
+	entry = create_tag(exif, EXIF_IFD_EXIF, EXIF_TAG_USER_COMMENT, 
+			sizeof(ASCII_COMMENT) + sizeof(FILE_COMMENT) - 2);
+	/* Write the special header needed for a comment tag */
+	memcpy(entry->data, ASCII_COMMENT, sizeof(ASCII_COMMENT)-1);
+	/* Write the actual comment text, without the trailing NUL character */
+	memcpy(entry->data+8, FILE_COMMENT, sizeof(FILE_COMMENT)-1);
+	/* create_tag() happens to set the format and components correctly for
+	 * EXIF_TAG_USER_COMMENT, so there is nothing more to do. */
+
+	/* Create a EXIF_TAG_SUBJECT_AREA tag */
+	entry = create_tag(exif, EXIF_IFD_EXIF, EXIF_TAG_SUBJECT_AREA,
+			   4 * exif_format_get_size(EXIF_FORMAT_SHORT));
+	entry->format = EXIF_FORMAT_SHORT;
+	entry->components = 4;
+	exif_set_short(entry->data, FILE_BYTE_ORDER, image_jpg_x / 2);
+	exif_set_short(entry->data+2, FILE_BYTE_ORDER, image_jpg_y / 2);
+	exif_set_short(entry->data+4, FILE_BYTE_ORDER, image_jpg_x);
+	exif_set_short(entry->data+6, FILE_BYTE_ORDER, image_jpg_y);
 
 	/* Get a pointer to the EXIF data block we just created */
 	exif_data_save_data(exif, &exif_data, &exif_data_len);
+	assert(exif_data != NULL);
 
 	f = fopen(FILE_NAME, "wb");
 	if (!f) {
@@ -181,7 +264,7 @@ int main(int argc, char **argv)
 		fprintf(stderr, "Error writing to file %s\n", FILE_NAME);
 		goto errout;
 	}
-	/* Write EXIF block length */
+	/* Write EXIF block length in big-endian order */
 	if (fputc((exif_data_len+2) >> 8, f) < 0) {
 		fprintf(stderr, "Error writing to file %s\n", FILE_NAME);
 		goto errout;
@@ -195,7 +278,7 @@ int main(int argc, char **argv)
 		fprintf(stderr, "Error writing to file %s\n", FILE_NAME);
 		goto errout;
 	}
-	/* Write JPEG image data */
+	/* Write JPEG image data, skipping the non-EXIF header */
 	if (fwrite(image_jpg+image_data_offset, image_data_len, 1, f) != 1) {
 		fprintf(stderr, "Error writing to file %s\n", FILE_NAME);
 		goto errout;
@@ -208,6 +291,10 @@ errout:
 		fprintf(stderr, "Error writing to file %s\n", FILE_NAME);
 		rc = 1;
 	}
+	/* The allocator we're using for ExifData is the standard one, so use
+	 * it directly to free this pointer.
+	 */
+	free(exif_data);
 	exif_data_unref(exif);
 
 	return rc;