Adding another io functions exercise for ch25

ex24_iofunctions03.c

@@ -0,0 +1,59 @@
+#include <stdio.h>
+#include "dbg.h"
+
+#define MAX_FILENAME 2048
+
+
+int main(int argc, char *argv[])
+{
+    int rc = -1;
+    char *filename;
+    int nchars = 0;
+    int nlines = 0;
+    int i;
+    long seekpos;
+    char c;
+    FILE *fp;
+
+    check(argc > 1, "You must provide a filename as arg 1");
+    filename = argv[1];
+
+    fp = fopen(filename, "r");
+    check(fp != NULL, "Failed to open \"%s\".", filename);
+
+    while((c = fgetc(fp)) != EOF) {
+        nchars++;
+        if (c == '\n') {
+            nlines++;
+            if (nlines % 10 == 0) {
+                printf("At line %d of \"%s\"\n", nlines, filename);
+            }
+        }
+    }
+
+    printf("\"%s\" contains %d chars\n", filename, nchars);
+
+    printf("Current position of \"%s\" is %ld\n", filename, ftell(fp));
+    printf("Writing out \"%s\" in reverse:\n", filename);
+
+    for (i = 0; i < nchars; i++) {
+        seekpos = (long)nchars - (i + 1);
+        rc = fseek(fp, seekpos, SEEK_SET);
+        check(rc != -1, "Failed to seek to %ld", seekpos);
+        c = fgetc(fp);
+        check(c != EOF, "Failed to read char at %ld", seekpos);
+        putc(c, stdout);
+    }
+
+    rewind(fp);
+    printf("\n\nRewound \"%s\" to position %ld\n", filename, ftell(fp));
+
+    rc = fclose(fp);
+    check(rc != -1, "Failed to close \"%s\".", filename);
+
+
+    return 1;
+
+error:
+    return 0;
+}