How can I pass a multidimensional array as a pointer in c

Question

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How to pass a multidimensional array to a function in C and C++

so I have char buffer[4][50]

I need to pass it to a method void SetBuffer(char **buffer) or at least that's how i think it's suppose to be formatted.

so I do SetBuffer(buffer);? In the method I need to set each element so

void SetBuffer(char **buffer)
{
strncpy(buffer[0], "something", 50);
strncpy(buffer[1], "something else", 50);
}

how can this be accomplished properly?

this looks more C to me then C++ – pyCthon Jun 06 '12 at 15:04 — pyCthon, Jun 06 '12 at 15:04

score 3 · Accepted Answer · answered Jun 06 '12 at 14:55

3

The C++ way would be to use a proper container (e.g. std::vector<unsigned char> or std::string) as appropriate.

OTOH, if there's a particular reason to fall back on arrays, using pointers (as you already do) and passing in the dimensions explicitly are one way to do it..

answered Jun 06 '12 at 14:55

dirkgently

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+1 for "use a proper container". I would have answered similarly. – Drise Jun 06 '12 at 14:56
best way to do it, I agree as I did a bit of research and saw that it was a dangerous design to use multidimensional array in this case – Pittfall Jun 06 '12 at 19:14

score 2 · Answer 2 · answered Jun 06 '12 at 14:58

2

There are many ways:

The easiest is:

void SetBuffer(char[][50] buffer)
{
strncpy(buffer[0], "something", 50);
strncpy(buffer[1], "something else", 50);

}

answered Jun 06 '12 at 14:58

Guy L

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score 2 · Answer 3 · answered Jun 06 '12 at 15:01

Caveat: this is a C answer. Your answer looks correct to me, but a better approach is something like:

#define BUFFER_DIM_1   4
#define BUFFER_DIM_2   50

int    i;
char **buffer;

/* Create an array of pointers to the lower level */
buffer = malloc(BUFFER_DIM_1 * sizeof(char *));
for (i=0; i<BUFFER_DIM_1; i++) {
    buffer[i] = malloc(BUFFER_DIM_2 * sizeof(char));
}

You can then use as you suggest.

for the braver of heart, you could go with only two mallocs and some cleverer pointer work:

#define BUFFER_DIM_1   4
#define BUFFER_DIM_2   50

int    i;
char **buffer;

/* Create an array of pointers to the lower level */
buffer    = malloc(BUFFER_DIM_1 * sizeof(char *));
buffer[0] = malloc(BUFFER_DUM_1 * BUFFER_DIM_2 * sizeof(char));
for (i=1; i<BUFFER_DIM_1; i++) {
    buffer[i] = buffer[i-1] + BUFFER_DIM_2 * sizeof(char);
}

Finally, don't forget to free all this memory up when you no longer need it.

That's fine in C, but in C++ use dirkgently answer – Guy L Jun 06 '12 at 15:02 — Guy L, Jun 06 '12 at 15:02

How can I pass a multidimensional array as a pointer in c

3 Answers3