Fix crash on adding items near book end

[xboard.git] / book.c

diff --git a/book.c b/book.c
index e42b9c6..6b1198d 100644 (file)
--- a/book.c
+++ b/book.c
@@ -676,8 +676,10 @@ void SaveToBook(char *text)
     if(count != currentCount) {
        do {
            for(i=0; i<len1; i++) buf2[i] = buf1[i]; len2 = len1;
-           fseek(f, readpos, SEEK_SET);
-           readpos += len1 = fread(buf1, 1, 4096, f);
+           if(readpos > writepos) {
+               fseek(f, readpos, SEEK_SET);
+               readpos += len1 = fread(buf1, 1, 4096, f);
+           } else len1 = 0; // wrote already past old EOF
            fseek(f, writepos, SEEK_SET);
            fwrite(buf2, 1, len2, f);
            writepos += len2;