Convert one dimensional string array to two dimensional string array in c

Question

char   *buffer;        /* holds the file contents. */
char   **transfer;
unsigned long    countNewLine = 0;
size_t  rowTrack;
size_t  columnTrack;

// assume countNewLine is 12

buffer_size = BUFSIZ;
buffer = malloc(buffer_size);
transfer = (char**)malloc(sizeof(char*)*sizeof(countNewLine));

columnTrack = 0;


while ( columnTrack < countNewLine ) {

    for ( rowTrack = 0; buffer[rowTrack] != '\n' || buffer[rowTrack] != '\0'; rowTrack++ )
        transfer[columnTrack][rowTrack] = buffer[rowTrack];

        columnTrack++;
}

I'm trying to convert 1D string array to 2D. I don't have any idea about my mistake. Thank you for solution.

Debugger result:

    buffer  char *  "first\nsecond\nthird\nfourth\nfifth\nsixth\nseventh\n
              eighth\nninth\ntenth\neleventh\ntwelfth\nthirteenth"  0x0000000100801200
    *buffer char    'f' 'f'
    countNewLine    unsigned long   12  12
    transfer    char ** 0x100105520 0x0000000100105520
    *transfer   char *  NULL    0x0000000000000000
    rowTrack    size_t  0   0
    columnTrack size_t  0   0

Standard Warning : Please [do not cast](http://stackoverflow.com/q/605845/2173917) the return value of `malloc()` and family. — Sourav Ghosh, Mar 10 '15 at 10:01
The loop will never terminate with `buffer[rowTrack] != '\n' || buffer[rowTrack] != '\0';` it should use `&&` and also, you have not allocated memory for each row of `*transfer[]`. — Weather Vane, Mar 10 '15 at 10:12
@WeatherVane Desktop/test/test/test/main.c:14:13: Definition of variable with array type needs an explicit size or an initializer for `char *transfer[]` — NewCoder, Mar 10 '15 at 10:16

Weather Vane · Accepted Answer · 2015-03-10T12:16:14.970

There are several errors in your code. In this line

transfer = (char**)malloc(sizeof(char*)*sizeof(countNewLine));

the second sizeof() is incorrect, the line should be

transfer = malloc(sizeof(char*) * countNewLine);

Next, you did not allocate memory for each row, which could be something like this

for ( rowTrack = 0; rowTrack < countNewLine; rowTrack++)
    transfer[rowTrack] = malloc(BUFSIZ);    // or whatever the line length is

The for loop will never terminate by using ||

for ( rowTrack = 0; buffer[rowTrack] != '\n' || buffer[rowTrack] != '\0'; rowTrack++ )

should be

for ( rowTrack = 0; buffer[rowTrack] != '\n' && buffer[rowTrack] != '\0'; rowTrack++ )

And lastly, I think you have your row and column indexing reversed in this statement:

transfer[columnTrack][rowTrack] = buffer[rowTrack];

There is a much cleaner way to split your string, like this:

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

#define BUFSIZ 512

int main(void) { 

    char *buffer;
    char *sptr;
    char **transfer = NULL;
    int rows = 0, row;

    /* ... load the file contents */
    buffer = malloc(BUFSIZ);
    strcpy (buffer, "first\nsecond\nthird\nfourth\nfifth\nsixth\nseventh\neighth\nninth\ntenth\neleventh\ntwelfth\nthirteenth");

    /* split the input */
    sptr = strtok(buffer, "\r\n");
    while (sptr) {
        transfer = realloc(transfer, (rows+1) * sizeof(char*));  // expand string array
        transfer[rows] = malloc(1+strlen(sptr));    // memory for string
        strcpy (transfer[rows], sptr);              // copy the token
        rows++;
        sptr = strtok(NULL, "\r\n");
    }

    /* show array */
    printf ("Showing %d rows\n", rows);
    for (row=0; row<rows; row++) {
        printf ("%s\n", transfer[row]);
        free (transfer[row]);                       // release mem
    }

    free (transfer);                                // release mem
    free (buffer);                                  // release mem
    return 0;
}

Program output:

Showing 13 rows
first
second
third
fourth
fifth
sixth
seventh
eighth
ninth
tenth
eleventh
twelfth
thirteenth

The comma in the condition does not do what (I think) you expect it to do: `for (...; expr1, expr2; ...)` — pmg, Mar 10 '15 at 11:10
`buffer = malloc(BUFSIZ);` or `transfer = malloc(BUFSIZ);` ? — NewCoder, Mar 10 '15 at 11:12
@pmg I expect both expressions to be true for the loop to proceed, please correct me if I am wrong. — Weather Vane, Mar 10 '15 at 11:17
@user3674483 `**transfer` is an array of pointers, equivalent to `*transfer[]` — Weather Vane, Mar 10 '15 at 11:17
no: `for (k = 0; 0, 1; k++)` is an infinite loop (unless there's a break inside): http://codepad.org/XNaniURQ — pmg, Mar 10 '15 at 12:03
@pmg thank you, in that case I edited the answer to use `&&` instead of `,` — Weather Vane, Mar 10 '15 at 12:16

Convert one dimensional string array to two dimensional string array in c

1 Answers1