whis is code segfaulting only outside of gdb [closed]

I have some code performing relatively simple operations

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <curses.h>

char map[3600] = {
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,
1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1
};
int getblock(int x,int y)
{
    

    
    return(map[x + 80 * y]);
}
int colread(char chr)
{
    switch(chr)
    {
        case 'k':
            return(COLOR_BLACK);
            break;
        case 'r':
            return(COLOR_RED);
            break;
        case 'g':
            return(COLOR_GREEN);
            break;
        case 'y':
            return(COLOR_YELLOW);
            break;
        case 'b':
            return(COLOR_BLUE);
            break;
        case 'm':
            return(COLOR_MAGENTA);
            break;
        case 'c':
            return(COLOR_MAGENTA);
            break;
        case 'w':
            return(COLOR_WHITE);
            break;

    }
        
}
void colinit()
{
    init_pair(0,COLOR_BLACK, COLOR_BLACK);
    init_pair(1,COLOR_BLACK,COLOR_WHITE);
    init_pair(3,COLOR_BLACK,COLOR_YELLOW);
    init_pair(26,COLOR_BLUE,COLOR_BLUE);
}
void colman(char bg,char fg)
{
    int bgint = colread(bg);
    int fgint = colread(fg);
    if(bgint == 0 && fgint == 1)
    {
        attrset(0);
        attron(A_BOLD);
    }
    else
    {
        attron(COLOR_PAIR(bgint*8+fgint));
    }
    
}
void pixrender(int x,int y){/*oh god please no*/
addstr("rendered pixel");refresh();
char coord[3];
sprintf(coord,"%d",x);
addstr("(");
addstr(coord);
addstr(",");
sprintf(coord,"%d",y);
addstr(coord);
addstr(")");
/*

b blue
r red
w white
k black
blue for blocks, white for spikes
*/
char fku = 'f';
char spritesheet[144] = {
//         0   1   2   3   4   5   6   7   8   9   0   1
/*empty */' ','x','n','v','d','b',' ',' ','-','_','[',']',
/*block */'*','X',fku,'V','d','b',' ',' ',fku,fku,'[',']',
/*spup  */'^','A','M','N','&','&',' ',' ','A',fku,'P','9',
/*spdwn */'Y',fku,'<','<','<','Z',' ',' ',fku,fku,fku,fku,
/*splft */'9','9','<','<','<','Z',' ',' ','<','<','<',fku,
/*sprht */'P','P','>','>','Z','>',' ',' ','>','>',fku,'>',
/*lava  */' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',
/*ice   */' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',
/*owup  */'~','~',fku,'T','Z','Z',' ',' ','~',fku,'[',']',
/*owdown*/'-','x','7','v','z','z',' ',' ','-','=','[',']',
/*owleft*/'[','[','9','Y','<','<',' ',' ','[','L','[','|',
/*owrht */']','h','R','j','>','>',' ',' ','[',']','|',']'
};
char bgsheet[144] = {
//         0   1   2   3   4   5   6   7   8   9   0   1
/*empty */'k','b','k','k','k','k','k','k','k','k','k','k',
/*block */'b','b',fku,'k','k','k','k','k',fku,fku,'k','k',
/*spup  */'k','k','k','k','k','k','k','k','k','k','k','k',
/*spdwn */'k',fku,'k','k','k','k','k','k',fku,fku,fku,fku,
/*splft */'k','k','k','k','k','k','k','k','k','k','k',fku,
/*sprht */'k','k','k','k','k','k','k','k','k','k',fku,'k',
/*lava  */'k','k','k','k','k','k','k','k','k','k','k','k',
/*ice   */'k','k','k','k','k','k','k','k','k','k','k','k',
/*owup  */'k','k',fku,'k','k','k','k','k','k',fku,'k','k',
/*owdown*/'k','k','k','k','k','k','k','k','k','k','k','k',
/*owleft*/'k','k','k','k','k','k','k','k','k','k','k','k',
/*owrht */'k','k','k','k','k','k','k','k','k','k','k','k',
};
char fgsheet[144] = {
//         0   1   2   3   4   5   6   7   8   9   0   1
/*empty */'k','b','w','w','w','w',' ',' ','y','y','y','y',
/*block */'b','b',fku,'w','w','w',' ',' ',fku,fku,'y','y',
/*spup  */'w','w','w','w','w','w',' ',' ','y',fku,'y','y',
/*spdwn */'w',fku,'w','w','w','w',' ',' ',fku,fku,fku,fku,
/*splft */'w','w','w','w','w','w',' ',' ','y','y','y',fku,
/*sprht */'w','w','w','w','w','w',' ',' ','y','y',fku,'y',
/*lava  */' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',
/*ice   */' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',' ',
/*owup  */'y','y',fku,'y','y','y',' ',' ','y',fku,'y','y',
/*owdown*/'y','y','y','y','y','y',' ',' ','-','y','y','y',
/*owleft*/'y','[','y','Y','y','y',' ',' ','y','y','y','y',
/*owrht */'y','h','y','y','y','y',' ',' ','y','y','y','y'
};
//segfault before here
int pos = getblock(x,2*y) + 12 * getblock(x,2*y+1);

colman(bgsheet[pos],fgsheet[pos]);
char cstr[2] = "";
cstr[0] = spritesheet[pos];
attron(A_BOLD);//why does this have to be here

addstr(cstr);
}
void render()
{
    int y = 24;
    int x;
    while (y >= 0)
    {
        x = 0;
        while(x < 80)
        {
            pixrender(x,y);
            x++;
        }
        if (y > 0)
        {
            addstr("n");
        }
        y-=1;
    }
    clear();
    refresh();
        
}

void game()
{

    colinit();
    while (true)
    {
        render();

    }
}
int main()
{
    
    initscr();

    
    start_color();
    attron(A_BOLD);
    game();
    endwin();
    return(0);

}

and it works…but only in gdb, when running the same a.out outside of gdb, it crashes due to a segfault, does anyone know what sort of interaction could cause this (or if its some specific code related issue), the most relevant thing I could find was https://www.reddit.com/r/cprogramming/comments/18k3o01/issue_with_segfault_when_running_code_outside_of/ but that it doesnt seem like there would be any latent memory issues, there also isnt any database stuff so there shouldnt be anything with fread, could it be an undefined behaviour of some sort?

  • c
  • gdb
  • ncurses

15

  1. Your program segfaults in getblock (x=48, y=49) on return(map[x + 80 * y]); aka return map[3968]; as you defined char map[3600] = {...}. It’s undefined behavior to access an array out of bounds. I don’t have any intuition as why it happens to work when your program is running under the control of gdb.

    It’s called from pixrender(x=48, y=24) which does int pos = getblock(x,2*y) + 12 * getblock(x,2*y+1). I don’t know what your program is supposed to do in order to propose a fix.

    valgrind is angry (there are also a few leaks):

    ==1804063== Invalid read of size 1
==1804063==    at 0x109210: getblock (1.c:35)
==1804063==    by 0x10A019: pixrender (1.c:138)
==1804063==    by 0x10A0D5: render (1.c:151)
==1804063==    by 0x10A141: game (1.c:165)
==1804063==    by 0x10A174: main (1.c:172)
==1804063==  Address 0x10e000 is not stack'd, malloc'd or (recently) free'd

  2. char map[3600] only stores 3600 bits so you could easily pack that into a uint8_t[3600/8] as you only access it via getblock(). 2 calls to memset() would be easier on the eyes. You also could run-length encode it. Or as it’s read-only get rid of entirely:

    int getblock(int x, int y) {
    assert(x >= 0 && x < 80);
    assert(y >= 0 && y < 45);
    return x + 80 * y >= 1600;
}

    People hate asserts here as you have the option of turning them off. I don’t turn them off and use them liberally for pre- and post-conditions. Use error checks if you have issues with assert. With the asserts you code now fails with:

    rendered pixela.out: 1.c:9: getblock: Assertion `y >= 0 && y < 45' failed.                                                       
                                                                Aborted

  3. Prefer symbolic constant instead of magic values (3600, 80, 24, 144). 3600 appears to be 80 * (40 + 5) or perhaps 80 * (2 * 24 + 1) but I don’t know why.

  4. Prefer to initialize arrays instead of separate assignment.

    char cstr[] = {spritesheet[pos], 0};

  5. Prefer to mark read-only variables const. It allows to more easily refactor code like I showed with map above.

  6. Prefer letting the compiler deduce the size of arrays.

    char spritesheet[] = {
   // ...
};

  7. Avoid global variables. It makes testing harder than necessary.

  8. Consider a struct xy { int x, int y } as you use or pass them as arguments.

  9. Consider an enum for the chr so the compiler can check you have a case for every value used.

  10. Prefer for to while loop for iteration. They are purpose built for it. In render():

    for(int y = 24; y >= 0; y--) {
    for(int x = 0; x < 80; x++)
        pixrender(x, y);
    // ...
}

  11. Minimize scope of variables. See previous.

0

Trang chủ Giới thiệu Sinh nhật bé trai Sinh nhật bé gái Tổ chức sự kiện Biểu diễn giải trí Dịch vụ khác Trang trí tiệc cưới Tổ chức khai trương Tư vấn dịch vụ Thư viện ảnh Tin tức - sự kiện Liên hệ Chú hề sinh nhật Trang trí YEAR END PARTY công ty Trang trí tất niên cuối năm Trang trí tất niên xu hướng mới nhất Trang trí sinh nhật bé trai Hải Đăng Trang trí sinh nhật bé Khánh Vân Trang trí sinh nhật Bích Ngân Trang trí sinh nhật bé Thanh Trang Thuê ông già Noel phát quà Biểu diễn xiếc khỉ Xiếc quay đĩa Dịch vụ tổ chức sự kiện 5 sao Thông tin về chúng tôi Dịch vụ sinh nhật bé trai Dịch vụ sinh nhật bé gái Sự kiện trọn gói Các tiết mục giải trí Dịch vụ bổ trợ Tiệc cưới sang trọng Dịch vụ khai trương Tư vấn tổ chức sự kiện Hình ảnh sự kiện Cập nhật tin tức Liên hệ ngay Thuê chú hề chuyên nghiệp Tiệc tất niên cho công ty Trang trí tiệc cuối năm Tiệc tất niên độc đáo Sinh nhật bé Hải Đăng Sinh nhật đáng yêu bé Khánh Vân Sinh nhật sang trọng Bích Ngân Tiệc sinh nhật bé Thanh Trang Dịch vụ ông già Noel Xiếc thú vui nhộn Biểu diễn xiếc quay đĩa Dịch vụ tổ chức tiệc uy tín Khám phá dịch vụ của chúng tôi Tiệc sinh nhật cho bé trai Trang trí tiệc cho bé gái Gói sự kiện chuyên nghiệp Chương trình giải trí hấp dẫn Dịch vụ hỗ trợ sự kiện Trang trí tiệc cưới đẹp Khởi đầu thành công với khai trương Chuyên gia tư vấn sự kiện Xem ảnh các sự kiện đẹp Tin mới về sự kiện Kết nối với đội ngũ chuyên gia Chú hề vui nhộn cho tiệc sinh nhật Ý tưởng tiệc cuối năm Tất niên độc đáo Trang trí tiệc hiện đại Tổ chức sinh nhật cho Hải Đăng Sinh nhật độc quyền Khánh Vân Phong cách tiệc Bích Ngân Trang trí tiệc bé Thanh Trang Thuê dịch vụ ông già Noel chuyên nghiệp Xem xiếc khỉ đặc sắc Xiếc quay đĩa thú vị

Filed under: Kiến thức lập trình - @ 18:33

Thẻ:

Trang chủ Giới thiệu Sinh nhật bé trai Sinh nhật bé gái Tổ chức sự kiện Biểu diễn giải trí Dịch vụ khác Trang trí tiệc cưới Tổ chức khai trương Tư vấn dịch vụ Thư viện ảnh Tin tức - sự kiện Liên hệ Chú hề sinh nhật Trang trí YEAR END PARTY công ty Trang trí tất niên cuối năm Trang trí tất niên xu hướng mới nhất Trang trí sinh nhật bé trai Hải Đăng Trang trí sinh nhật bé Khánh Vân Trang trí sinh nhật Bích Ngân Trang trí sinh nhật bé Thanh Trang Thuê ông già Noel phát quà Biểu diễn xiếc khỉ Xiếc quay đĩa
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