Strange output when using system("clear") command in C program - c

Question

I have the following code
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <time.h>
#include <stdbool.h>
#define dimensions 5
int RandomNumInRange(int M, int N)
{
return M + rand() / (RAND_MAX / (N - M + 1) + 1);
}
char ** CreateWorld(int dim)
{
int i,j;
char **world = malloc(dim *sizeof(char*));
for(i=0;i<dim;i++)
world[i]=malloc(dim*sizeof(char));
for(i=0;i<dim;i++)
for(j=0;j<dim;j++)
world[i][j]=42;
return world;
}
void CreateCastle(char **world)
{
//assuming world is big enough
//to hold a match of 2
int randRow,randCol;
//1 to dimension -2 so we can spawn a 3x3 castle
randRow = RandomNumInRange(1,dimensions-2);
randCol = RandomNumInRange(1,dimensions-2);
printf("position: %d %d\n", randRow, randCol);
world[randRow][randCol]='c';
//fill the rest so castle is 3x3
//assuming there is enough space for that
world[randRow-1][randCol-1]=35;
world[randRow-1][randCol]=35;
world[randRow-1][randCol+1]=35;
world[randRow][randCol-1]=35;
world[randRow][randCol+1]=35;
world[randRow+1][randCol-1]=35;
world[randRow+1][randCol]=35;
world[randRow+1][randCol+1]=35;
}
void DisplayWorld(char** world)
{
int i,j;
for(i=0;i<dimensions;i++)
{
for(j=0;j<dimensions;j++)
{
printf("%c",world[i][j]);
}
printf("\n");
}
}
int main(void){
system("clear");
int i,j;
srand (time(NULL));
char **world = CreateWorld(dimensions);
DisplayWorld(world);
CreateCastle(world);
printf("Castle Positions:\n");
DisplayWorld(world);
//free allocated memory
free(world);
//3 star strats
char ***world1 = malloc(3 *sizeof(char**));
for(i=0;i<3;i++)
world1[i]=malloc(3*sizeof(char*));
for(i=0;i<3;i++)
for(j=0;j<3;j++)
world1[i][j]="\u254B";
for(i=0;i<3;i++){
for(j=0;j<3;j++)
printf("%s",world1[i][j]);
puts("");
}
free(world1);
//end
return 0 ;
}
If I use the system("clear") command, I get a line consisting of "[3;J"
followed by an expected output. If I run the program again, I get the same gibberish, then many blank newlines, then the expected output. If I put the system("clear") command in comments then both the "[3;J" and the blank newlines don't show and the output is expected.
Edit: it seems the error is not in the code, but rather in the way the terminal on my system is (not) set. Thank you all for your input, I definitely have a lot of interesting stuff to read and learn now.

Answer 1

The codes being sent by your clear command from don't seem to be compatible with the Gnome terminal emulator, which I believe is what you would be using.
The normal control codes to clear a console are CSI H CSI J. (CSI is the Control Sequence Initializer: an escape character \033 followed by a [). CSI H sends the cursor to the home position, and CSI J clears from the cursor position to the end of the screen. You could also use CSI 2 J which clears the entire screen.
On Linux consoles and some terminal emulators, you can use CSI 3 J to clear both the entire screen and the scrollback. I would consider it unfriendly to do this (and the clear command installed on my system doesn't.)
CSI sequences can typically contain semicolons to separate numeric arguments. However, the J command doesn't accept more than one numeric argument and the semicolon seems to cause Gnome terminal to fail to recognize the control sequence. In any event, I don't believe Gnome terminal supports CSI 3 J.
The clear command normally uses the terminfo database to find the correct control sequences for the terminal. It identifies the terminal by using the value of the TERM environment variable, which suggests that you have to wrong value for that variable. Try setting export TERM=xterm and see if you get different results. If that works, you'll have to figure out where Linux Mint configures environment variables and fix it.
On the whole, you shouldn't need to use system("clear") to clear your screen; it's entirely too much overhead for such a simple task. You would be better off using tputs from the ncurses package. However, that also uses the terminfo database, so you will have to fix your TERM setting in any case.