Passing two dimensional array in function

[salman83]

Hi all,
I want to pass two dimensional array in a function. The function is publicly exposed, so array length cannot be static. I want to check if the function signature is correct.

void Display(int rows, int cols, const char *const *paramValues)
{
int i;

for( i = 0; i < (rows * cols); i++ )
{
printf( "paramValues[%d] = %s\n", i, paramValues[i] );
}
}


int main( int nargs, char *args[] )
{
char *paramVals[5][2];

char a[5][10] = { "Test_1", "Test_2", "Test_3", "Test_4", "Test_5" };
char b[5][10] = { "Hello_1", "Hello_2", "Hello_3", "Hello_4", "Hello_5" };

int i;

for( i = 0; i < 5; i++ )
{
paramVals[i][0] = a[i];
paramVals[i][1] = b[i];

}


Display( 5, 2, paramVals);

return 0;
}

[Tavo]

Let me ask you a couple of questions:

1) Why do you access de bidimension array like this: nameArr[]. It is WRONG! First of all, it is bidimensional, and second you are using pointers (Well a const-pointer that is a reference and a pointer).
2) Why do you use a const-pointer? I mean, it isn´t bad at all, but I would use a pointer-pointing a pointer.

[laserlight]

Have you considered using std::string or some other string class along with std::vector or some other container?

Why do you access de bidimension array like this: nameArr[]. It is WRONG!

It is okay, especially in this context since we are dealing with an array of null terminated strings.

[Tavo]

Have you considered using std::string or some other string class along with std::vector or some other container?

It would be wonderful you do that, specially when you are dealing with strings, string+vector is a power combination ^^!

It is okay, especially in this context since we are dealing with an array of null terminated strings.

Really? I don´t know that, well, I learn something new.

[SivakumarT]

Hi,

This is an excellent thread.

When you are passing the 2-dimensional array to a function, the function declaration will atleast require to specify the second dimension size. While you pass the pointer to the 2-d array also, you may have to specify the second dimension size.

If you dont specify the size of the 2nd dimension, the array subscript missing error comes.

I listed few cases below to my knowledge:

// method 1: 2-d array
void PrintA(char a[][10])
{
	for (int i=0; i<5; i++)
		printf("\n%s", a[i]);
}

// method 2: 2-d array
void PrintAA(char (*a)[10])
{
	for (int i=0; i<5; i++)
		printf("\n%s", a[i]);
}

// method 1: Pointer to 2-d array
void PrintPVal(char *p[5][2])
{
	for (int i=0; i<5; i++)
	{
		printf("\n%s\t%s", p[i][0], p[i][1]);
	}
}

// method 2: Pointer to 2-d array
void PrintPVal(char *p[][2])
{
	for (int i=0; i<5; i++)
	{
		printf("\n%s\t%s", p[i][0], p[i][1]);
	}
}

int main()
{
	char a[5][10] = { "Test_1", "Test_2", "Test_3", "Test_4", "Test_5" };
	char b[5][10] = { "Hello_1", "Hello_2", "Hello_3", "Hello_4", "Hello_5" };

	PrintA(a);

	PrintAA(a);

	char* pval[5][2];

	for (int i=0; i<5; i++)
	{
		pval[i][0] = a[i];
		pval[i][1] = b[i];
	}

	PrintPVal(pval);

	return 0;
}

-Siva