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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.
This commit is contained in:
Vladimir Panteleev 2017-09-19 14:33:51 +00:00 committed by Michael Stapelberg
parent da72a5be91
commit 4ddf18ef6b
1 changed files with 3 additions and 4 deletions
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7
src/fake_outputs.c
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@ -33,10 +33,10 @@ static Output *get_screen_at(unsigned int x, unsigned int y) {
* *
*/ */
void fake_outputs_init(const char *output_spec) { void fake_outputs_init(const char *output_spec) {
char useless_buffer[1024];
const char *walk = output_spec; const char *walk = output_spec;
unsigned int x, y, width, height; 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", DLOG("Parsed output as width = %u, height = %u at (%u, %u)\n",
width, height, x, y); width, height, x, y);
Output *new_output = get_screen_at(x, y); Output *new_output = get_screen_at(x, y);
@ -68,8 +68,7 @@ void fake_outputs_init(const char *output_spec) {
num_screens++; num_screens++;
} }
/* Figure out how long the input was to skip it */ walk += chars_consumed + 1;
walk += sprintf(useless_buffer, "%ux%u+%u+%u", width, height, x, y) + 1;
} }
if (num_screens == 0) { if (num_screens == 0) {