Dynamic Memory Allocation - c

Question

I'm having trouble dynamically allocating memory for an array. I've been debugging for hours, any pointers?
I posted the rest of the code. It is simply supposed to exchange the swap the first row with the second, and the third with the forth. I am getting strange results like:
Enter string: hello
Enter string: how are you
Enter string: i'm good thanks
Enter string: bye
Enter string: bai
Enter string: xx
=========================
how are you
!i'm good thanks
hello
!how are you
bye
!bai
i'm good thanks
!bye
bai
!xx
int count = 0;
char *lines[MAX_LINES];
char *tmp[50];
printf("Enter string: ");
fgets(tmp, 50, stdin);
lines[count] = (char *) malloc((strlen(tmp)+1) * sizeof(char));
strcpy(lines[count], tmp);
while(strcmp("xx\n", lines[count])){
count++;
printf("Enter string: ");
fgets(tmp, 50, stdin);
lines[count] = (char *) malloc((strlen(tmp)+1)* sizeof(char));
strcpy(lines[count], tmp);
}
void exchange(char * records[])
{
char * temp;
temp = records[0];
records[0] = records[1];
records[1] = temp;
temp = records[2];
records[2] = records[3];
records[3] = temp;
}
void printArray(char * inputs[], int row, int col)
{
int i, j;
for(i = 0; i < row; i++){
for(j = 0; j < col; j++){
printf("%c", inputs[i][j]);
}
}
}

Answer 1

This code seems to work:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
enum { MAX_LINES = 50 };
static void printArray(char *inputs[], int rows);
static int readLine(char *buffer, size_t buflen);
int main(void)
{
int count = 0;
char *lines[MAX_LINES];
char tmp[50];
for (count = 0; count < MAX_LINES; count++)
{
if (readLine(tmp, sizeof(tmp)) == EOF)
break;
lines[count] = (char *) malloc((strlen(tmp)+1)* sizeof(char));
if (lines[count] == 0)
break;
strcpy(lines[count], tmp);
}
putchar('\n');
printArray(lines, count);
return(0);
}
static int read_line(char *buffer, size_t buflen)
{
printf("Enter string: ");
if (fgets(buffer, buflen, stdin) == 0 || strcmp("xx\n", buffer) == 0)
return EOF;
return 0;
}
static void printArray(char *inputs[], int rows)
{
for (int i = 0; i < rows; i++)
printf("%d: %s", i, inputs[i]);
}
Sample run 1 (using EOF):
$ ./rl
Enter string: Abyssinia
Enter string: Wimbledon Common
Enter string: ^D
0: Abyssinia
1: Wimbledon Common
$
Sample run 2 (using 'xx'):
$ ./rl
Enter string: Abyssinia
Enter string: Wimbledon Common
Enter string: Strawberry Lemonade
Enter string: xx
0: Abyssinia
1: Wimbledon Common
2: Strawberry Lemonade
$
What's different? I fixed the type on tmp as noted in a comment. I created a function readLine() to manage the prompt and read and compare with "xx\n" process to avoid repetition. I avoided using strdup() but do check that malloc() succeeds before using the pointer returned. I ensure that there are not too many lines read in (the for loop). The printArray() code only takes the number of rows because the strings are of varying length. I removed the exchange() function since it was not being used and I couldn't see how it was supposed to be used. The code is complete and compilable (so it is an SSCCE — Short, Self-Contained, Correct Example).