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Concatenate double pointer char array in C

There are many questions about how to concatenate char array in C, but what I want to know is different from that. I would like to know how to concatenate "double pointer" char array in C.

For example,

const char *array1 = "aa", "bb";
const char *array2 = "cc", "dd", "ee";


I want to get the new double pointer array of char like this:

char **new_array = "aa", "bb", "cc", "dd", "ee";
// this code actually doesn't work, though


I want to know the simplest and fastest way to realize this.

EDIT: In fact, I am planning to create a program below.

int main(int argc, char **argv)
pid_t pid;
char **args = "sh", "-c" + argv; // this code doesn't work
posix_spawn(&pid, "/bin/sh", NULL, NULL, (char* const*)args, NULL);



This program just passes arguments after "sh -c".

strcat

2 Answers
2

Sure, just allocate a buffer for that

#define _GNU_SOURCE 1
#include <stdio.h>
#include <strings.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
int main()

#define ARRAY_SIZE(x) (sizeof(x) / sizeof(x[0]))
const char * const array1 = "aa", "bb";
const size_t array1_size = ARRAY_SIZE(array1);
const char * const array2 = "cc", "dd", "ee";
const size_t array2_size = ARRAY_SIZE(array2);
const size_t concat_len = array1_size + array2_size;
const char ** const concat = malloc(concat_len * sizeof(*concat));

assert(concat != NULL);
for (size_t i = 0; i < concat_len; ++i)
concat[i] = strdup(i < array1_size ? array1[i] : array2[i - array1_size]);
assert(concat[i] != NULL);


for (size_t i = 0; i < concat_len; ++i)
printf("concat[%zu] = (%zu) '%s'n", i, strlen(concat[i]), concat[i]);


for (size_t i = 0; i < concat_len; ++i)
free(concat[i]);

free(concat);

return 0;



But we should be able to do better.

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

void main()

const char *array1 = "aa", "bb";
const char *array2 = "cc", "dd", "ee";


int arraySize1 = (sizeof(array1)/sizeof(char*));
int arraySize2 = (sizeof(array2)/sizeof(char*));
char **resultArr = (char **)malloc(sizeof(char *)*(arraySize1+arraySize2));
int i =0;

/* copy array1*/
for(i=0;i<arraySize1;i++)

resultArr[i] = malloc(strlen(array1[i]) +1);
strcpy(resultArr[i], array1[i]);


/*copy array2*/
for(i=0;i<arraySize2;i++)

resultArr[arraySize1+i] = malloc(strlen(array2[i])+1);
strcpy(resultArr[arraySize1+i], array2[i]);


/*print resulting array*/
for(i=0;i<arraySize1+arraySize2;i++)

printf("%s ", *(resultArr+i));




malloc(sizeof(array1[i]))

sizeof(array1[i])

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