How to convert a 1 dimensional array buffer to a 2 dimensonal format

I have this intermediary buffer that has the entire contents of a file: char *intermediary_buffer

I need to move this to a different 2D buffer: char **final_buffer Where a new row is started every time the \n escape sequence is detected in the original buffer. Effectively storing each line of the file in its own row.

I thought about using a for loop, where it would scan through the intermediary buffer and copy every part leading up to the \n escape sequence in a row:

for(int i = 0; i < file_size; i++){
  if(intermediary_buffer[i] == '\n'){
    // Copy all leading up to `\n` to new 2D buffer
  }
}

I get lost after creating the for loop . . .

How can I achieve this in a fast way?

One option is to iterate through the memory block that contains the file contents using strcspn. Allocate pointers and allocate memory to each pointer. realloc can allocate pointers and strndup will handle the allocation of memory to each pointer and copy data to the allocated memory.

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

#define SIZE 8129

char **strpdlm ( char *source, char *delim) {
    char **target = NULL; // pointer to pointer
    int span = 0;
    int count = 0;

    while ( source && *source) {
        span = strcspn ( source, delim); // count to next delimiter

        char **temp = NULL;
        if ( NULL == ( temp = realloc ( target, sizeof target * ( count + 2)))) { // allocate two more pointers
            fprintf ( stderr, "realloc problem\n");
            return target;
        }

        target = temp;

        if ( NULL == ( target[count] = strndup ( source, span + 1))) { // allocate memory and copy to one pointer
            fprintf ( stderr, "strndup problem\n");
            return target;
        }

        ++count;
        target[count] = NULL; // the other pointer serves as sentinel NULL

        source += span; // advance pointer
        if ( *source) { // not at terminating zero
            ++source; // advance past delimiter
        }
    }

    return target;
}

char *readcontents ( char *filename) {
    char *contents = NULL;
    char buffer[SIZE] = "";
    size_t size = 0;
    size_t bytes = 0;
    FILE *pf = NULL;

    if ( NULL == ( pf = fopen ( filename, "r"))) {
        perror ( filename); // why the file could not be opened
        return contents;
    }

    while ( 0 < ( bytes = fread ( buffer, 1, sizeof buffer, pf))) { // read a buffer from file
        char *temp = NULL;
        if ( NULL == ( temp = realloc ( contents, size + bytes + 1))) { // reallocate contents for buffer
            fprintf ( stderr, "problem realloc\n");
            fclose ( pf);
            return contents;
        }
        contents = temp;
        memmove ( contents + size, buffer, bytes); // append buffer to contents
        size += bytes;
        contents[size] = 0; // terminating zero
    }

    fclose ( pf);

    return contents;
}

int main ( void) {
    char *filename = "file.txt";
    char *contents = NULL;
    char *delim = "\n";
    char **lines = NULL;

    if ( NULL == ( contents = readcontents ( filename))) {
        fprintf ( stderr, "no contents in file %s\n", filename);
        return 1;
    }

    printf ( "contents\n%s\n", contents);

    if ( NULL == ( lines = strpdlm ( contents, delim))) {
        free ( contents);
        fprintf ( stderr, "strpdlm returned NULL\n");
        return 1;
    }

    free ( contents); // free contents

    size_t each = 0;
    printf ( "\nlines\n");
    while ( lines[each]) { // not at sentinel NULL
        printf ( "lines[%zu]%s", each, lines[each]);
        ++each;
    }
    printf ( "\n");

    each = 0;
    while ( lines[each]) { // not at sentinel NULL
        free ( lines[each]); // free pointer memory
        ++each;
    }
    free ( lines); // free pointers

    return 0;
}