From: Vladimir Panteleev <git@thecybershadow.net>
Date: Tue, 19 Sep 2017 14:33:51 +0000 (+0000)
Subject: fake_outputs: Use %n format specifier instead of sprintf
X-Git-Tag: 4.15~72^2~3
X-Git-Url: https://git.sur5r.net/?a=commitdiff_plain;h=755b22327807593fd184c4dae46b197848a74452;p=i3%2Fi3

fake_outputs: Use %n format specifier instead of sprintf

fake_outputs_init used a sprintf invocation with a throw-away buffer
to estimate how many characters the sscanf invocation consumed. This
was unnecessary, and also potentially incorrect, as differences
between the read and formatted strings (such as leading zeros) could
lead to fake_outputs_init to lose its track.

Instead, use the %n format specifier which allows saving the number of
characters consumed by sscanf so far. %n is part of C99.
---

diff --git a/src/fake_outputs.c b/src/fake_outputs.c
index 6639b361..447409d2 100644
--- a/src/fake_outputs.c
+++ b/src/fake_outputs.c
@@ -33,10 +33,10 @@ static Output *get_screen_at(unsigned int x, unsigned int y) {
  *
  */
 void fake_outputs_init(const char *output_spec) {
-    char useless_buffer[1024];
     const char *walk = output_spec;
     unsigned int x, y, width, height;
-    while (sscanf(walk, "%ux%u+%u+%u", &width, &height, &x, &y) == 4) {
+    int chars_consumed;
+    while (sscanf(walk, "%ux%u+%u+%u%n", &width, &height, &x, &y, &chars_consumed) == 4) {
         DLOG("Parsed output as width = %u, height = %u at (%u, %u)\n",
              width, height, x, y);
         Output *new_output = get_screen_at(x, y);
@@ -68,8 +68,7 @@ void fake_outputs_init(const char *output_spec) {
             num_screens++;
         }
 
-        /* Figure out how long the input was to skip it */
-        walk += sprintf(useless_buffer, "%ux%u+%u+%u", width, height, x, y) + 1;
+        walk += chars_consumed + 1;
     }
 
     if (num_screens == 0) {