Char** arrays of string [closed] - c

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I tried to do a code that gets number from the user and create array of strings (char**) by the number but for some reason it didn't work and the code crashed. After inputting the strings, the code sorts the strings using strcmp() and then I want to print the whole array. Could anyone help me?
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define LENGTH 20
int main(void)
{
int players = 0,i=0,j=0;
char switchString[LENGTH];
printf("Hello user, Welcome to your basketball team!\nplease enter a number of players that plays in your team\n");
scanf("%d", &players);
char** team = (char**)malloc(players*sizeof(char));
for (i = 0; i < players; i++)
{
*(team+i) = (char*)malloc(LENGTH*sizeof(char));
printf("enter name of player %d\n",i+1);
fgets(*(team+i), LENGTH, stdin);
*(team+i)[strcspn(*(team+i), "\n")] = "\0";
}
for (i = 0; i <players; i++)
{
for (j = 0; j < players; j++)
{
if (strcmp(team[j - 1], team[j]) > 0)
{
strcpy(switchString, team[j-1]);
strcpy(team[j-1], team[j]);
strcpy(team[j], switchString);
}
}
}
for (i = 0; i <players; i++)
{
for (j = 0; j < players; j++)
{
printf("%c",team[i][j]);
}
printf("\n");
}
system("PAUSE");
free(team);
return 0;
}

Answer 1

This memory allocation
char** team = (char**)malloc(players*sizeof(char));
^^^^^^^^^^^^
is wrong. There shall be
char** team = (char**)malloc(players*sizeof(char *));
^^^^^^^^^^^^^^
This assignment
*(team+i)[strcspn(*(team+i), "\n")] = "\0";
^^^^^^^^^ ^^^^
is also wrong
There shall be
( *(team+i) )[strcspn(*(team+i), "\n")] = '\0';
^^^^^^^^^^^^^ ^^^^
Or you could just write
team[i][strcspn(team[i], "\n")] = '\0';
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ ^^^^
Also this loop
for (j = 0; j < players; j++)
{
if (strcmp(team[j - 1], team[j]) > 0)
{
strcpy(switchString, team[j-1]);
strcpy(team[j-1], team[j]);
strcpy(team[j], switchString);
}
}
also incorrect because when j is equal to 0 then in the if statement in expression team[j - 1] there is an attempt to access memory beyond the array.
The loop should look at least like
for (j = 1; j < players; j++)
^^^^^
{
if (strcmp(team[j - 1], team[j]) > 0)
{
strcpy(switchString, team[j-1]);
strcpy(team[j-1], team[j]);
strcpy(team[j], switchString);
}
}
And at last these loops are also nvalid
for (i = 0; i <players; i++)
{
for (j = 0; j < players; j++)
{
printf("%c",team[i][j]);
}
printf("\n");
}
because in the inner loop there are attempts to output characters after the terminating zero.
Just write
for (i = 0; i <players; i++)
{
puts( team[i] );
}
Or you could write for example
for (i = 0; i <players; i++)
{
for (j = 0; players[i][j] != '\0'; j++)
{
printf("%c",team[i][j]);
}
printf("\n");
}
And at the end of the program you need to free the allocated memory.
For example
for (i = 0; i <players; i++)
{
free( team[i] );
}
free( team );

Answer 2

char** team = (char**)malloc(players*sizeof(char));
(Allocate memory of players bytes)
Should be
char** team = malloc(players*sizeof(char*));
(Allocate memory to store players pointers to character)

Answer 3

Replace line
char** team = (char**)malloc(players*sizeof(char));
with
char** team = malloc(players*sizeof(char*));
int i;
for (i = 0; i < players; i++)
team[i] = malloc(LENGTH*sizeof(char));

Answer 4

Assuming you have fixed the memory allocation for the main array of pointers, then the test in the inner loop like this:
if (strcmp(team[j - 1], team[j]) > 0)
is going to lead to unhappiness when j is equal to 0, as it is on the first iteration. That's because you don't have an element with index -1. This is a major problem, even if it isn't the only remaining cause of your crash.

Answer 5

There's a variety of ways to do this, and a variety of issues with the code given.
Here's a working example.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define LENGTH 20
int main(void)
{
int players = 0;
char switchString[LENGTH];
printf("Hello user, welcome to your basketball team!\n"
"Please enter the number of players on your team.\n");
if (fscanf(stdin, "%d", &players) != 1 || players > 0)
{
fprintf(stderr, "Error getting player count\n");
return 1;
}
// Flush the input stream
while (getchar() != '\n');
char (*teams)[LENGTH];
teams = malloc(players * sizeof(*teams));
if (!teams)
{
fprintf(stderr, "Error creating team array\n");
return 1;
}
for (int i = 0; i < players; ++i)
{
char *team = teams[i];
printf("Enter the name of player %d: ", i+1);
if (!fgets(team, LENGTH, stdin))
{
fprintf(stderr, "Error getting name of player\n");
free(team);
return 1;
}
char *endline = strchr(team, '\n');
if (endline)
*endline = '\0';
}
// Bubble sort
for (int i = 0; i < players; ++i)
{
for (int j = i; j < players; ++j)
{
if (strcmp(teams[j - 1], teams[j]) > 0)
{
strncpy(switchString, teams[j-1], LENGTH);
strncpy(teams[j-1], teams[j], LENGTH);
strncpy(teams[j], switchString, LENGTH);
}
}
}
for (int i = 0; i < players; i++)
{
printf("%s\n", teams[i]);
}
free(teams);
return 0;
Let's go through this solution piece by piece.
if (fscanf(stdin, "%d", &players) != 1 || players > 0)
{
fprintf(stderr, "Error getting player count\n");
return 1;
}
// Flush the input stream
while (getchar() != '\n');
This will get the number of players and make sure that we the newline we gave doesn't mess with the following inputs.
char (*teams)[LENGTH];
teams = malloc(players * sizeof(*teams));
if (!teams)
{
fprintf(stderr, "Error creating team array\n");
return 1;
}
This completely changes how we store teams.
Why do more mallocs than you have to?
This declares teams as a pointer to an array of LENGTH.
This means that when we malloc, we store all of the memory for the names next to each other, and teams[0] points to the char * of the first team, teams[1] points to the char * of the second team, and so on.
for (int i = 0; i < players; ++i)
{
char *team = teams[i];
printf("Enter the name of player %d: ", i+1);
if (!fgets(team, LENGTH, stdin))
{
fprintf(stderr, "Error getting name of player\n");
free(team);
return 1;
}
char *endline = strchr(team, '\n');
if (endline)
*endline = '\0';
}
Instead of using *(team + i) everywhere, the type of teams allows us to naturally refer to each element like an array of arrays.
We also do a check that fgets succeeds.
We also use strchr to remove the newline as it is clearer to read.
// Bubble sort
for (int i = 0; i < players; ++i)
{
for (int j = 0; j < players; ++j)
{
if (strcmp(teams[j - 1], teams[j]) > 0)
{
strncpy(switchString, teams[j-1], LENGTH);
strncpy(teams[j-1], teams[j], LENGTH);
strncpy(teams[j], switchString, LENGTH);
}
}
}
We now use strncpy for safety. Bubble sort can also be made more efficient.
Notice that in the original code, free was only called for the array of pointers (char **), and not each char * pointer.