array of pointers to pointers how to initialize the correct and concise way of doing it and using it-CodePudding

I like to know that I have data which are in pair of two strings so there are a list of pair of two strings. like

{{"<html","</html>"},{"<head","</head>"}}

So I want to define pointer variable as is array of pointers to pointers so pointers will be pointing to pointers that points to strings (should be char *) like string <html is pointed by pointer *tags_1[0] and </html> is pointed to by what, I may be completely wrong? this is a question. But first I like to know how to define or construct this array of pointers to pointers like initialiing it with above {{"<html","</html>"},{...}} for tags_1

I tried like char **tags_1[2]={{"<html","</html>"},{"<head","</head>"}}; but this obviously wrong but I can do this if I have array of pointers static char *tags[] = {"<html","<head","<body","<div","<h1","<h2","<h3","<h4","<h5","<br", "<span","<input","<footer","<section","<table","<tr","<td","<a","<button","<end"};

so my question is how to define like assigning initialized values to array of pointers to pointers then how to use them especially comparing string <html and </html> indexed elements with strncmp of array of pointers to pointers and printf and assigning character to each indexed of string (char *). Can anyone please tell me this

CodePudding user response：

A concise way to allocate is to use a Pointer-to-Array-of char*[2], e.g.

char *(*tags)[2];

That way you can use a single allocation for however many pairs you have, and easily realloc if you need more. A short example would be:

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

int main (void) {
  
  char *(*tags)[2] = malloc (2 * sizeof *tags);
  
  tags[0][0] = "<html";
  tags[0][1] = "</html>";
  tags[1][0] = "<head";
  tags[1][1] = "</head>";
  
  for (int i = 0; i < 2; i  ) {
    for (int j = 0; j < 2; j  )
      printf (" %s", tags[i][j]);
    putchar ('\n');
  }
  
  free (tags);
  
}

Example Use/Output

$ ./bin/ptr2arrcharstar
 <html </html>
 <head </head>

Let me know if you have further questions.

CodePudding user response：

For this you don't need an array of pointers to pointers.

What you need is an array of array of char-pointers. It looks like:

const char* tags[][2] = {{"<html","</html>"},{"<head","</head>"}};

Now you can do stuff like:

printf("%s\n", tags[0][0]);  // prints <html
printf("%s\n", tags[1][1]);  // prints </head>

and

char str[] = "some_text";
if (strcmp(str, tags[1][0]) == 0) // Check if str equals <head
{
    // Match
}