How is buffer processing causing different behaviors? - c

Question

The context
I have written a program which takes two coordinates as input and modifies an ASCII world map based on where those coordinates land (land or water):
#include <stdio.h>
#define ROW 22
#define COL 73
#define EMPTY ' '
#define FILLED '.'
#define LAND '#'
#define WATER '~'
void initialize(char map[][COL]);
void show(char map[][COL]);
void colorArea(char map[][COL], int, int, char, char);
int main(void) {
char map[ROW][COL];
char type;
int r, c;
initialize(map);
show(map);
while(1) {
do {
printf("\nMax = (%d, %d). Per uscire inserire (0, 0).\n"
"Inserire le coordinate e premere invio: ", COL, ROW);
scanf("%d%d", &c, &r);
} while (r > ROW || c > COL);
if (r < 1 || c < 1) {
printf("Arrivederci!\n");
return 0;
}
for (int i = 0; i < 100; i++)
putchar('\n'); // Clear the screen.
type = map[--r][--c]; // Could be WATER, LAND, FILLED or EMPTY.
if (type == EMPTY)
colorArea(map, r, c, type, WATER);
else if (type == FILLED)
colorArea(map, r, c, type, LAND);
else if (type == LAND)
colorArea(map, r, c, type, FILLED);
else if (type == WATER)
colorArea(map, r, c, type, EMPTY);
map[r][c] = 'X'; // Mark the point on the map.
show(map);
}
return 0;
}
void initialize(char map[][COL]) {
char *s[ROW];
int r, c;
s[0] = " .. ";
s[1] = " ... .. ........ .. ";
s[2] = " ............... .. ....... ............... ";
s[3] = " ................. ... .... .. ...................... ";
s[4] = " .. ................... . .. ........................... ";
s[5] = " ................ .. ............................ ";
s[6] = " ............. ........ ........................... ";
s[7] = " ...... . .................................... . ";
s[8] = " ... ... . .......................... .. ";
s[9] = " ... . ..... ...................... . ";
s[10] = " .. .................. ............ ";
s[11] = " ..... ........... . .... ... ";
s[12] = " ......... ........ .. ... ";
s[13] = " ........... ...... . ";
s[14] = " . ......... ..... . .. ";
s[15] = " ....... .... . ........ ";
s[16] = " ...... .. ............ ";
s[17] = " .... .... ..... . ";
s[18] = " .. .. .. ";
s[19] = " . . ";
s[20] = " ";
s[21] = " ";
for (r = 0; r < ROW; r++)
for (c = 0; c < COL; c++)
map[r][c] = s[r][c];
}
// Print the map.
void show(char map[][COL]) {
int r, c;
printf("\n /");
for (c = 0; c < COL; c++)
printf("–");
printf("\\\n");
for (r = 0; r < ROW; r++) {
printf(" |");
for (c = 0; c < COL; c++)
printf("%c", map[r][c]);
printf("|\n");
}
printf(" \\");
for (c = 0; c < COL; c++)
printf("–");
printf("/\n");
}
void colorArea(char map[][COL], int r, int c, char type, char color) {
if (c > COL || r > ROW)
return;
if (map[r][c] == type) {
map[r][c] = color;
colorArea(map, r+1, c, type, color); // Down.
colorArea(map, r-1, c, type, color); // Up.
colorArea(map, r, c+1, type, color); // Right.
colorArea(map, r, c-1, type, color); // Left.
}
}
The problem(s)
Changing the content of printf alters the behavior of the program. If I remove the spacing characters from the show function (which prints the map one character away from the left margin) it works unexpectedly:
void show(char map[][COL]) {
int r, c;
printf("/");
for (c = 0; c < COL; c++)
printf("-");
printf("\\\n");
for (r = 0; r < ROW; r++) {
printf("|");
for (c = 0; c < COL; c++)
printf("%c", map[r][c]);
printf("|\n");
}
printf("\\");
for (c = 0; c < COL; c++)
printf("-");
printf("/");
}
but if doing so I also translate the first printf in English
printf("\nMax = (%d, %d). Enter (0, 0) to exit.\n"
"Enter the coordinates: ", COL, ROW);
it behaves again as it should. Of course the problem is the language, it's probably due to shortness of the English version, but I can't figure out why. A picture is worth a thousand words, so here it is (the second one is the one with the strange behavior):
Note that this only happens when the coordinates land on water (for example (1, 1)) and the content of printf is displayed again if I hit the water again, which make it even more confusing to me. Furthermore, if I enter (0, 0) to exit the program after the problem occurs, the program does exit but returns 139 (segmentation fault), but I don't get how it's possible since there is a check with a return 0; before calling any function.
What I figured
Buffer behavior is not standardized. Often buffers process one line at a time, and mine works this way (I tested it with another program). Sometimes characters like \n are left in the buffer and cause unwanted behaviors, but it shouldn't be the case here: scanf scans for integers, so it should ignore space characters (unlike when it scans for char).
The question(s)
What's causing the problem? What are the two dots that appear? What is happening to the buffer in each step?

Answer 1

you access out of your array including doing assignment producing undefined behavior, do :
void colorArea(char map[][COL], int r, int c, char type, char color) {
if (c >= COL || r >= ROW || c < 0 || r < 0)
and
void colorEverything(char map[][COL], int r, int c) {
if (c >= COL || r >= ROW || c < 0 || r < 0)
Also in show in printf("-"); the minus is not the simple ASCII character minus but a complex sequence of character probably produced by your editor (under Windows ?)