One more exercise with IO functions.

ex24_iofunctions06.c

@@ -0,0 +1,57 @@
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include "dbg.h"
+
+
+int main(int argc, char *argv[])
+{
+    int fd;
+    int rc;
+    long lrc;
+    char *out;
+    char buffer[1024];
+    fpos_t pos;
+    FILE *instream;
+    FILE *outstream;
+
+    check(argc == 2, "You must provide a filename.");
+
+    fd = open(argv[1], O_RDWR | O_CREAT);
+    check(fd != -1, "Unable to open \"%s\" for reading and writing.", argv[1]);
+
+    rc = fchmod(fd, 0644);
+    check(rc != -1, "Failed to chmod \"%s\"", argv[1]);
+
+    outstream = fdopen(fd, "w");
+    check(outstream != NULL, "Unable to open an outstream.");
+
+    rc = fgetpos(outstream, &pos);
+    check(rc != -1, "Failed to get position of outstream.");
+
+    rc = fprintf(outstream, "It was written.");
+    check(rc > 0, "Failed to write to outstream.");
+
+    rc = fflush(outstream);
+    check(rc != EOF, "Failed to flush outstream.");
+
+    rc = fsetpos(outstream, &pos);
+    check(rc != -1, "Failed to set outstream back to old position.");
+
+    instream = fdopen(fd, "r");
+    check(instream != NULL, "Unable to open an instream.");
+
+    rewind(instream);
+    lrc = ftell(instream);
+    check(lrc == 0, "Failed to rewind instream.");
+
+    out = fgets(buffer, 1023, instream);
+    check(buffer != NULL, "Failed to read from instream.");
+
+    printf("Read this from instream: \"%s\"\n", buffer);
+
+    return 0;
+error:
+    return 1;
+}