Program received signal EXC_BAD_ACCESS - Mac OS X - c++

Question

When I'm comparing an element in std::vector to char, I randomly get this error sometimes when running to program (about once every five times):
Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: 13 at address: 0x0000000000000000
0x0000000100017c49 in randomCaveGenerator (p=#0x7fff5fbff51c, q=#0x7fff5fbff518, seed=1234567) at src/main.cpp:198
198 if (lm.map[1][i][j] == '0')
v is defined as a std::vector with all elements filled. I know this error usually means it is pointing to a null pointer but I know there shouldn't be one.
I'm using Mac OS X 10.8, gdb to debug, and Apple LLVM version 4.2 (based on LLVM 3.2svn) to compile.
Edit
The code that I'm using:
typedef std::vector< std::vector<char> > MapGrid;
struct LevelMap
{
std::string name;
std::vector<MapGrid> map;
sf::Vector2u size;
};
LevelMap randomCaveGenerator(int p=64, int q=64, unsigned long seed=1)
{
if (p < 64)
p = 64;
if (q < 64)
q = 64;
int groundLevel = 12;
srand(seed);
sf::Vector2u size(p, q);
std::vector<MapGrid> mapG(3);
for (int i = 0; i < 3; i++)
{
mapG[i] = MapGrid(size.x, std::vector<char>(size.y));
for (int y = 0; y < size.y; y++)
{
for (int x = 0; x < size.x; x++)
{
mapG[i][x][y] = '0';
}
}
}
for (int y = 0; y < size.y; y++)
{
for (int x = 0; x < size.x; x++)
{
mapG[0][x][y] = 'v'; // Void Tile
}
}
for (int y = 0; y < size.y; y++)
{
for (int x = 0; x < size.x; x++)
{
mapG[2][x][y] = '0'; // Air Tile
}
}
for (int y = groundLevel; y < size.y; y++)
{
for (int x = 0; x < size.x; x++)
{
int e = 23;
if (2+(rand()%e)< e/2)
mapG[1][x][y] = 'd';
else
mapG[1][x][y] = '0';
}
}
LevelMap lm;
lm.name = "Random Map";
lm.map = mapG;
lm.size = size;
for (int i = 0; i < 12; i++)
doSimStep(lm);
for (int i = 1; i < lm.size.x - 2; i++)
{
for (int j = 1; j < 12+groundLevel; j++)
{
if (lm.map[1][i][j] == '0') // PART WHERE THE ERROR IS
continue;
else
{
lm.map[1][i][j] = 'g';
lm.map[2][i][j-1] = 'w';
i++;
j = 1;
}
}
}
for (int i = 1; i < lm.size.x - 2; i++)
{
for (int j = groundLevel; j < lm.size.y - 2; j++)
{
if (lm.map[1][i][j] == 'd')
{
if (rand()%120 == 0)
lm.map[2][i][j] = 'p';
}
}
}
for (int i = 0; i < lm.size.y; i++)
{
lm.map[1][0][i] = 'X';
lm.map[1][lm.size.x-2][i] = 'X';
lm.map[2][0][i] = '0';
lm.map[2][lm.size.x-2][i] = '0';
}
for (int i = 0; i < lm.size.x; i++)
{
lm.map[1][i][0] = 'X';
lm.map[1][i][lm.size.y-2] = 'X';
lm.map[2][i][0] = '0';
lm.map[2][i][lm.size.y-2] = '0';
}
return lm;
}

Answer 1

With no source code apart from the error message
if (v[i] == '0')
I can only imagine i >= v.size()
You might want to consider using iterators to access your vector, so you don't step off the end.