Programming Forums > Application Development > C++

Harakim · Jun 5th, 2006, 5:52 PM

Although this isn't technically true "char *name" and "char name[xx]" are basically the same.

When you are passing an array in C, you can pass it as a pointer and dereference it with brackets.

(Toggle Plain Text)

int foo( char *bar )
{
	bar[1] = 100;
}


int foo2()
{
	char bar2[20];
	
	foo( bar2 );	

	//bar2[1] now equals 100
}

I have heard that they are not the same at all, so hopefully someone will be enraged by my saying they are and come and explain it. As for passing arrays though, I'm pretty sure that should work.

(Toggle Plain Text)

int foo( char **bar )
{
	bar[1][2] = 100;
}


int foo2()
{
	char bar2[20][10];
	
	foo( bar2 );	

	//bar2[1][2] now equals 100
}

EDIT: fixed error in code

DaWei · Jun 5th, 2006, 5:57 PM

Quote:

"char *name" and "char name[xx]" are basically the same.

This isn't true. They are essentially different. I use the term, 'essentially', advisedly. One only has to use them as if they are the same (even in a valid way) and examine the emitted code. The compiler tends to hide this difference in some instances, as a perceived favor to the user. Sometimes, if one accepts it literally, as many seem to do these days, it isn't a favor. You might want to refer to the section in my tutorial on pointers (see my sig) entitled, "What is NOT a pointer".

Manan · Jun 13th, 2006, 10:14 PM

I've decided to use a template, because I have way too little time to actually do a totally random generator. But I'm having another problem declaring 2d arrays.

(Toggle Plain Text)

if(randTemplate == 1)
	{ //If template 2 is chosen
		int buffer[9][9] = {

             {n[6],n[7],n[8], n[1],n[0],n[4], n[2],n[5],n[3] },
             {n[1],n[4],n[5], n[2],n[8],n[3], n[6],n[0],n[7] },
             {n[2],n[0],n[3], n[5],n[7],n[6], n[4],n[1],n[8] },

             {n[8],n[2],n[1], n[7],n[6],n[0], n[5],n[3],n[4] },
             {n[5],n[3],n[0], n[4],n[2],n[8], n[1],n[7],n[6] },
             {n[7],n[6],n[4], n[3],n[1],n[5], n[8],n[2],n[0] },

             {n[0],n[5],n[7], n[8],n[4],n[2], n[3],n[6],n[1] },
             {n[4],n[1],n[2], n[6],n[3],n[7], n[0],n[8],n[5] },
             {n[3],n[8],n[6], n[0],n[5],n[1], n[7],n[4],n[2] }
          };
}

The above segment of code works perfectly. However, I want to declare int buffer[][] outside the if statement. This is because, it is currently a local variable and I want to use it outside the if statement. Here is what I'm trying to do:

(Toggle Plain Text)

int buffer[9][9];
if(randTemplate == 1)
	{ //If template 2 is chosen
		buffer[][] = {

             {n[6],n[7],n[8], n[1],n[0],n[4], n[2],n[5],n[3] },
             {n[1],n[4],n[5], n[2],n[8],n[3], n[6],n[0],n[7] },
             {n[2],n[0],n[3], n[5],n[7],n[6], n[4],n[1],n[8] },

             {n[8],n[2],n[1], n[7],n[6],n[0], n[5],n[3],n[4] },
             {n[5],n[3],n[0], n[4],n[2],n[8], n[1],n[7],n[6] },
             {n[7],n[6],n[4], n[3],n[1],n[5], n[8],n[2],n[0] },

             {n[0],n[5],n[7], n[8],n[4],n[2], n[3],n[6],n[1] },
             {n[4],n[1],n[2], n[6],n[3],n[7], n[0],n[8],n[5] },
             {n[3],n[8],n[6], n[0],n[5],n[1], n[7],n[4],n[2] }
          };
}

I get about 50-60 errors when I do this. I've even tried getting rid of the [][], and I also tried making it [9][9], but it won't work. Help is greatly appreciated

nindoja · Jun 13th, 2006, 11:20 PM

After you declare the array you cannot use an initializer list to declare the values. You will have to either loop through or have individual assignments.

The Dark · Jun 13th, 2006, 11:32 PM

Or you could try something like:

(Toggle Plain Text)

int buffer[9][9];
if(randTemplate == 1)
	{ //If template 2 is chosen
	     int buffer2[9][9] = {

             {n[6],n[7],n[8], n[1],n[0],n[4], n[2],n[5],n[3] },
             {n[1],n[4],n[5], n[2],n[8],n[3], n[6],n[0],n[7] },
             {n[2],n[0],n[3], n[5],n[7],n[6], n[4],n[1],n[8] },

             {n[8],n[2],n[1], n[7],n[6],n[0], n[5],n[3],n[4] },
             {n[5],n[3],n[0], n[4],n[2],n[8], n[1],n[7],n[6] },
             {n[7],n[6],n[4], n[3],n[1],n[5], n[8],n[2],n[0] },

             {n[0],n[5],n[7], n[8],n[4],n[2], n[3],n[6],n[1] },
             {n[4],n[1],n[2], n[6],n[3],n[7], n[0],n[8],n[5] },
             {n[3],n[8],n[6], n[0],n[5],n[1], n[7],n[4],n[2] }
             };
             memcpy (buffer, buffer2, sizeof buffer);
      }

Manan · Jun 14th, 2006, 1:57 AM

Thanks, but what does the function memcpy() do? Does it assign buffer2 to buffer?

The Dark · Jun 14th, 2006, 2:14 AM

Google Is Your Friend

Manan · Jun 14th, 2006, 2:16 AM

Cool, thanks.

Manan · Jun 14th, 2006, 6:55 PM

Wow, memcpy is actually way better than simply assigning matrices through 2 nested for loops. Thanks, it really shortened my code by about 30 lines.

The Dark · Jun 14th, 2006, 7:48 PM

Note that you only want to do it for simple types, once you start having classes in your matrices, you have to be careful that you don't muck up any allocated pointers.

Jun 5th, 2006, 5:52 PM	#21
Harakim Hobbyist Programmer Join Date: May 2006 Location: West Jordan, Utah, United States Posts: 176 Rep Power: 3	Although this isn't technically true "char name" and "char name[xx]" are basically the same. When you are passing an array in C, you can pass it as a pointer and dereference it with brackets. (Toggle Plain Text) int foo( char bar ) { bar[1] = 100; } int foo2() { char bar2[20]; foo( bar2 ); //bar2[1] now equals 100 } int foo( char bar ) { bar[1] = 100; } int foo2() { char bar2[20]; foo( bar2 ); //bar2[1] now equals 100 } I have heard that they are not the same at all, so hopefully someone will be enraged by my saying they are and come and explain it. As for passing arrays though, I'm pretty sure that should work. (Toggle Plain Text) int foo( char bar ) { bar[1][2] = 100; } int foo2() { char bar2[20][10]; foo( bar2 ); //bar2[1][2] now equals 100 } int foo( char *bar ) { bar[1][2] = 100; } int foo2() { char bar2[20][10]; foo( bar2 ); //bar2[1][2] now equals 100 } EDIT: fixed error in code

Jun 13th, 2006, 10:14 PM	#23
Manan Newbie Join Date: May 2006 Posts: 13 Rep Power: 0	I've decided to use a template, because I have way too little time to actually do a totally random generator. But I'm having another problem declaring 2d arrays. (Toggle Plain Text) if(randTemplate == 1) { //If template 2 is chosen int buffer[9][9] = { {n[6],n[7],n[8], n[1],n[0],n[4], n[2],n[5],n[3] }, {n[1],n[4],n[5], n[2],n[8],n[3], n[6],n[0],n[7] }, {n[2],n[0],n[3], n[5],n[7],n[6], n[4],n[1],n[8] }, {n[8],n[2],n[1], n[7],n[6],n[0], n[5],n[3],n[4] }, {n[5],n[3],n[0], n[4],n[2],n[8], n[1],n[7],n[6] }, {n[7],n[6],n[4], n[3],n[1],n[5], n[8],n[2],n[0] }, {n[0],n[5],n[7], n[8],n[4],n[2], n[3],n[6],n[1] }, {n[4],n[1],n[2], n[6],n[3],n[7], n[0],n[8],n[5] }, {n[3],n[8],n[6], n[0],n[5],n[1], n[7],n[4],n[2] } }; } if(randTemplate == 1) { //If template 2 is chosen int buffer[9][9] = { {n[6],n[7],n[8], n[1],n[0],n[4], n[2],n[5],n[3] }, {n[1],n[4],n[5], n[2],n[8],n[3], n[6],n[0],n[7] }, {n[2],n[0],n[3], n[5],n[7],n[6], n[4],n[1],n[8] }, {n[8],n[2],n[1], n[7],n[6],n[0], n[5],n[3],n[4] }, {n[5],n[3],n[0], n[4],n[2],n[8], n[1],n[7],n[6] }, {n[7],n[6],n[4], n[3],n[1],n[5], n[8],n[2],n[0] }, {n[0],n[5],n[7], n[8],n[4],n[2], n[3],n[6],n[1] }, {n[4],n[1],n[2], n[6],n[3],n[7], n[0],n[8],n[5] }, {n[3],n[8],n[6], n[0],n[5],n[1], n[7],n[4],n[2] } }; } The above segment of code works perfectly. However, I want to declare int buffer[][] outside the if statement. This is because, it is currently a local variable and I want to use it outside the if statement. Here is what I'm trying to do: (Toggle Plain Text) int buffer[9][9]; if(randTemplate == 1) { //If template 2 is chosen buffer[][] = { {n[6],n[7],n[8], n[1],n[0],n[4], n[2],n[5],n[3] }, {n[1],n[4],n[5], n[2],n[8],n[3], n[6],n[0],n[7] }, {n[2],n[0],n[3], n[5],n[7],n[6], n[4],n[1],n[8] }, {n[8],n[2],n[1], n[7],n[6],n[0], n[5],n[3],n[4] }, {n[5],n[3],n[0], n[4],n[2],n[8], n[1],n[7],n[6] }, {n[7],n[6],n[4], n[3],n[1],n[5], n[8],n[2],n[0] }, {n[0],n[5],n[7], n[8],n[4],n[2], n[3],n[6],n[1] }, {n[4],n[1],n[2], n[6],n[3],n[7], n[0],n[8],n[5] }, {n[3],n[8],n[6], n[0],n[5],n[1], n[7],n[4],n[2] } }; } int buffer[9][9]; if(randTemplate == 1) { //If template 2 is chosen buffer[][] = { {n[6],n[7],n[8], n[1],n[0],n[4], n[2],n[5],n[3] }, {n[1],n[4],n[5], n[2],n[8],n[3], n[6],n[0],n[7] }, {n[2],n[0],n[3], n[5],n[7],n[6], n[4],n[1],n[8] }, {n[8],n[2],n[1], n[7],n[6],n[0], n[5],n[3],n[4] }, {n[5],n[3],n[0], n[4],n[2],n[8], n[1],n[7],n[6] }, {n[7],n[6],n[4], n[3],n[1],n[5], n[8],n[2],n[0] }, {n[0],n[5],n[7], n[8],n[4],n[2], n[3],n[6],n[1] }, {n[4],n[1],n[2], n[6],n[3],n[7], n[0],n[8],n[5] }, {n[3],n[8],n[6], n[0],n[5],n[1], n[7],n[4],n[2] } }; } I get about 50-60 errors when I do this. I've even tried getting rid of the [][], and I also tried making it [9][9], but it won't work. Help is greatly appreciated

Jun 13th, 2006, 11:32 PM	#25
The Dark Expert Programmer Join Date: Jun 2005 Posts: 824 Rep Power: 4	Or you could try something like: (Toggle Plain Text) int buffer[9][9]; if(randTemplate == 1) { //If template 2 is chosen int buffer2[9][9] = { {n[6],n[7],n[8], n[1],n[0],n[4], n[2],n[5],n[3] }, {n[1],n[4],n[5], n[2],n[8],n[3], n[6],n[0],n[7] }, {n[2],n[0],n[3], n[5],n[7],n[6], n[4],n[1],n[8] }, {n[8],n[2],n[1], n[7],n[6],n[0], n[5],n[3],n[4] }, {n[5],n[3],n[0], n[4],n[2],n[8], n[1],n[7],n[6] }, {n[7],n[6],n[4], n[3],n[1],n[5], n[8],n[2],n[0] }, {n[0],n[5],n[7], n[8],n[4],n[2], n[3],n[6],n[1] }, {n[4],n[1],n[2], n[6],n[3],n[7], n[0],n[8],n[5] }, {n[3],n[8],n[6], n[0],n[5],n[1], n[7],n[4],n[2] } }; memcpy (buffer, buffer2, sizeof buffer); } int buffer[9][9]; if(randTemplate == 1) { //If template 2 is chosen int buffer2[9][9] = { {n[6],n[7],n[8], n[1],n[0],n[4], n[2],n[5],n[3] }, {n[1],n[4],n[5], n[2],n[8],n[3], n[6],n[0],n[7] }, {n[2],n[0],n[3], n[5],n[7],n[6], n[4],n[1],n[8] }, {n[8],n[2],n[1], n[7],n[6],n[0], n[5],n[3],n[4] }, {n[5],n[3],n[0], n[4],n[2],n[8], n[1],n[7],n[6] }, {n[7],n[6],n[4], n[3],n[1],n[5], n[8],n[2],n[0] }, {n[0],n[5],n[7], n[8],n[4],n[2], n[3],n[6],n[1] }, {n[4],n[1],n[2], n[6],n[3],n[7], n[0],n[8],n[5] }, {n[3],n[8],n[6], n[0],n[5],n[1], n[7],n[4],n[2] } }; memcpy (buffer, buffer2, sizeof buffer); }

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Jun 13th, 2006, 11:20 PM	#24
nindoja Programmer Join Date: Jun 2005 Posts: 92 Rep Power: 4	After you declare the array you cannot use an initializer list to declare the values. You will have to either loop through or have individual assignments.

Jun 14th, 2006, 1:57 AM	#26
Manan Newbie Join Date: May 2006 Posts: 13 Rep Power: 0	Thanks, but what does the function memcpy() do? Does it assign buffer2 to buffer?

Jun 14th, 2006, 2:14 AM	#27
The Dark Expert Programmer Join Date: Jun 2005 Posts: 824 Rep Power: 4	Google Is Your Friend

Jun 14th, 2006, 2:16 AM	#28
Manan Newbie Join Date: May 2006 Posts: 13 Rep Power: 0	Cool, thanks.

Jun 14th, 2006, 6:55 PM	#29
Manan Newbie Join Date: May 2006 Posts: 13 Rep Power: 0	Wow, memcpy is actually way better than simply assigning matrices through 2 nested for loops. Thanks, it really shortened my code by about 30 lines.

Jun 14th, 2006, 7:48 PM	#30
The Dark Expert Programmer Join Date: Jun 2005 Posts: 824 Rep Power: 4	Note that you only want to do it for simple types, once you start having classes in your matrices, you have to be careful that you don't muck up any allocated pointers.

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