Program for work with arrays in dynamic memory.
Need equivalent for C. Can anybody help?
const int n = 6;
char **words = (char**) malloc(n *sizeof(char*));
for(int i = 0 ; i < n; i++)
words[i] = (char*)malloc( 50 * sizeof(int));
for(int i = 0; i < n; i++)
{
cin>>words[i];
}
cout<<endl;
for(int i = 0; i < n; i++)
{
if(words[i][0] == 'q')
cout<<words[i]<<endl;
}
The only C++ parts there are cin and cout; you can change them easily:
cin>>words[i];
becomes
scanf("%s", words[i]);
or
gets(words[i]);
while
cout<<words[i]<<endl;
becomes
puts(words[i]);
By the way, in the cin/scanf/gets you have a potential buffer overflow, since you are allocating space for 6 characters but you are accepting input of any length. You should do instead:
scanf("%6s", words[i]);
or (more maintainable, since it uses n directly)
fgets(words[i], n, stdin);
(although this will include the trailing \n in the string)
The only C++ features you are using are cin and cout. replace cin>>words[i] with gets(words[i]) and cout<<words[i]<<endl with puts(words[i]).
Use scanf("%s", &words[i]) to input data from stdin and printf("%s\n", words[i]) to output to stdout.
As you wish:
const int n = 6;
char **words = (char**) malloc(n *sizeof(char*));
int i = 0;
for( i= 0 ; i < n; i++)
{
words[i] = (char*)malloc( 50 * sizeof(char));
}
for(i = 0; i < n; i++)
{
scanf("%s", words[i]);
}
printf("\n");
for(i = 0; i < n; i++)
{
if(words[i][0] == 'q')
printf("%s\n", words[i]);
}
Related
I don't know why but my code prints a list of (null)(null)(null)....
I have to print the list of words from a file 'words.txt'.
Another question is: fscanf ignore white spaces?
#define WORD_LENGTH 1024
#define SIZE_QUOTE 100
int main(){
char **quote = malloc(sizeof(char*) * (size_t)SIZE_QUOTE);
long i;
for(i = 0; i < SIZE_QUOTE; i++){
if(!(malloc(sizeof(char) * (size_t)WORD_LENGTH)))
exit(1);
}
i = 0;
FILE *pf = fopen("words.txt", "r");
while(!feof(pf) && i < SIZE_QUOTE){
fscanf(pf, "%s", quote[i]);
printf("%s", quote[i]);
i++;
}
fclose(pf);
free(quote);
}
You're never assigning the return value of malloc() to quote[i] so they end up staying NULL (if you're lucky):
char **quote = malloc(sizeof(char*) * (size_t)SIZE_QUOTE);
long i;
for(i = 0; i < SIZE_QUOTE; i++){
if(!(malloc(sizeof(char) * WORD_LENGTH)))
It should be something like this instead:
char **quote = malloc(sizeof(char*) * (size_t)SIZE_QUOTE);
for(int i = 0; i < SIZE_QUOTE; i++){
quote[i] = malloc(sizeof(char) * WORD_LENGTH);
if(!quote[i])
Also you could avoid malloc() entirely and statically initialize that array if all the sizes are known:
char quote[SIZE_QUOTE][WORD_LENGTH] = {{'\0'}};
Also, you should be free()-ing the individual quote[i] at the end too:
for(int i = 0; i < SIZE_QUOTE; ++i) free(quote[i]);
free(quote);
There's other mistakes that have been pointed out through the comments already, so I won't elaborate further.
Can you please help me with fixing below code. Not sure where the segmentation fault is.
char str[] = "00ab00,00cd00";
char **strptr;
int i;
strptr = malloc(sizeof(char*) * 2);
strcnt = 0;
int j=0;
for(i=0;i<sizeof(str);i++) {
char c = *(str+i);
printf("%c", c);
if(c==',') {
strcnt++;
j=0;
}
strptr[strcnt][j++] = c;
}
Please ignore my poor coding :)
PS: I know its possible to split using strtok() easily.
Not sure where the segmentation fault is
As others have mentioned in the comments, you are not assigning memory to the pointers strptr[0] and strptr[1] but, you are trying to access them. This leads to segmentation fault.
Use a for loop to initially assign memory to strptr[0] and strptr[1]
strptr = malloc(sizeof(char*) * 2);
for(i = 0; i < 2; i++) //here, initialise each to 1 byte
{
strptr[i] = malloc(1);
}
strcnt = 0;
Here's a question on how to initialise a pointer to a pointer.
then, resize them at each step as you add additional character using the realloc() function.
for(i = 0, j = 0; i < sizeof(str); i++)
{
strptr[strcnt] = realloc(strptr[strcnt], j + 2);
//here, you resize each time to provide space for additional character using realloc()
char c = *(str + i);
printf("%c", c);
if(c == ',')
{
++strcnt;
j=0;
continue; //use a continue here
}
strptr[strcnt][j] = c;
strptr[strcnt][++j] = '\0';
//to provide null terminating character at the end of string (updated to next position at every iteration)
}
don't forget to free() the allocated memory
for( i=0; i<2; i++)
{
printf("%s\n", strptr[i]); //just to display the string before `free`ing
free(strptr[i]);
}
free(strptr);
Altogether your code would be something like this:
char str[] = "00ab00,00cd00";
char **strptr;
int i, j;
int strcnt;
strptr = malloc(sizeof(char*) * 2);
for(i = 0; i < 2; i++)
{
strptr[i] = malloc(1);
}
strcnt = 0;
for(i = 0, j = 0; i < sizeof(str); i++)
{
strptr[strcnt] = realloc(strptr[strcnt], j + 2);
char c = *(str + i);
printf("%c", c);
if(c == ',')
{
++strcnt;
j=0;
continue;
}
strptr[strcnt][j] = c;
strptr[strcnt][++j] = '\0';
}
for( i=0; i<2; i++)
{
printf("%s\n", strptr[i]);
free(strptr[i]);
}
free(strptr);
return 0;
int main(void)
{
int howMany,i,j;
char* temp = NULL;
char** friends = NULL;
printf("Please enter the number of the friends you have\n");
scanf(" %d",&howMany);
howMany++;
friends = (char**) malloc(sizeof(char*)*howMany);
for (i = 0; i < howMany; i++)
{
temp = (char*) malloc(20*sizeof(char));
fgets(temp,20,stdin);
temp[strspn(temp, "\n")] = '\0';
*(friends + i) = (char*)realloc(temp,sizeof(char) * (strlen(temp)+1));
}
for (i = 0; i < howMany; i++)
{
for ( j = 0; j < strlen(*(friends+i)); j++)
{
printf("%c",friends[i][j]);
}
printf("\n");
}
for (i = 0; i < howMany; i++)
{
free(*(friends + i));
}
free(friends);
getchar();
return 0;
}
The purpose of my code is to get the amount of friends i have, their names and finally printing it to the screen, any ideas why my code isn't working?
Input:
2
daniel
david
Output:
(\n)
Expected output:
daniel
david
The main problem is here:
temp[strspn(temp, "\n")] = '\0';
You used the wrong function. You want strcspn, not strspn. Change it to:
temp[strcspn(temp, "\n")] = '\0';
Also, as others pointed out, you should not change the value of howMany, since you need its original value in your loops.
So basically what my program did before i had to change it so that it would accept arbitrary values, was to take x-amount of words and the size of the words would also be arbitrary. (both are user inputted). I did this via a multiArray.
Then sorted according to alphabetical-order.
I'm just going to put it out there as my code is shit and I'm very unfamiliar with the usage of arbitrary-strings and pointers. I've read up on it in the manual but the concept needs to sink in a little bit first i believe. Anyhow, I get the error: "Abort trap: 6" when i run the program. Could anyone please help me fix this problem so that i can see how the code would look like if it was actually working, i think that would help me understand both pointers and allocating memory a lot better. Forever in debt if you do.
Current code:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#define MAX_LENGTH 10
int main(){ //8
char *name;
char tname[] = {0};
char temp[] = {0};
int i=0, j=0, n=0;
ssize_t bytes_read;
size_t bytes_number;
printf("Enter the amount of words you want to input: ");
scanf("%d", &n);
printf("Enter %d words: ",n);
bytes_number = MAX_LENGTH;
name = (char *) malloc (bytes_number+ 1);
bytes_number = 0;
bytes_read = getline(&name, &bytes_number, stdin);
if (bytes_read == -1){
puts("ERROR!");
free(name);
}
for (i = 0; i < n; i++){
strcpy(&tname[i], &name[i]);
}
for (i = 0; i < n - 1 ; i++){
for ( j = i + 1; j < n; j++){
if (strcmp(&name[i], &name[j]) > 0){
strcpy(temp, &name[i]);
strcpy(&name[i], &name[j]);
strcpy(&name[j], temp);
}
}
}
printf("\n------------------------------------------\n");
printf("%-3s %4s %11s\n", "Input","|", "Output");
printf("------------------------------------------\n");
for (i = 0; i < n; i++)
{
printf("%s\t\t%s\n", &tname[i], &name[i]);
}
printf("------------------------------------------\n");
}
This
strcpy(&tname[i], &name[i]);
is completely wrong, if you just want to copy all the characters, then it's just
strcpy(tname, name);
which is equivalent to
for (size_t i = 0 ; name[i] != '\0' ; ++i)
tname[i] = name[i];
using strcpy(&tname[i], &name[i]) is wrong because it will copy all the bytes from name until '\0' is found, at every loop starting at the i-th character.
But this will fail again because tname is does not have room, it's an array with just one element.
Since you want to sort the strings, you DO NOT NEED TO COPY them. Just swap the pointers. Also
char temp[] = {0};
only allocates 1 character, thus
strcpy(temp, name);
will invoke Undefined Behavior.
Try this, maybe it's what you need
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int
main(void)
{
char **words;
char *temp;
int word_count;
int actual_count;
char *word;
size_t length;
int result;
printf("Enter the amount of words you want to input: ");
if (scanf("%d%*c", &word_count) != 1)
return -1; // Input error
printf("Enter '%d' words:\n", word_count);
words = NULL;
word = NULL;
result = -1;
actual_count = 0;
length = 0;
for (int i = 0 ; i < word_count ; ++i)
{
char **pointer;
printf("Word(%d) > ", i + 1);
if ((length = getline(&word, &length, stdin)) <= 0)
goto cleanup;
// Grow the array of words
pointer = realloc(words, (i + 1) * sizeof(*pointer));
if (pointer == NULL)
goto cleanup; // Memory Exhausted
// Now it's safe to overwrite `words'
words = pointer;
words[i] = malloc(length);
if (words[i] == NULL)
goto cleanup; // Memory Exhausted
memcpy(words[i], word, length);
words[i][length - 1] = '\0'; // Replace '\n' with '\0'
actual_count += 1;
}
printf("Input : ");
for (int i = 0 ; i < actual_count ; ++i)
printf("%s\t", words[i]);
printf("\n");
for (int i = 0; i < actual_count - 1 ; i++)
{
for (int j = i + 1 ; j < actual_count ; ++j)
{
if (strcmp(words[i], words[j]) <= 0)
continue;
temp = words[i];
words[i] = words[j];
words[j] = temp;
}
}
printf("Output: ");
for (int i = 0 ; i < actual_count ; ++i)
printf("%s\t", words[i]);
printf("\n");
result = 0;
cleanup:
free(word);
for (int i = 0; i < actual_count ; i++)
free(words[i]);
free(words);
return result;
}
Note: This would consider an empty word (made completely of white space characters), as a valid word.
This is the code:
I do know what is the problem, I tried for hours to fix it, but was not successful
#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
void input(char ***array1,int * sizeWords,int size)
{
for (int i = 0; i < size; i++)
{
char word[81] = "";
char descrip[201] = "";
int numAgdarot = 0;
//how mach agdarot
printf("how mach of agdarrot you want? ");
scanf("%d", &numAgdarot);
//save the count of agdarot
sizeWords[i] = numAgdarot;
do
{
printf("enter word number %d: ", i);
_flushall();
gets(word);
} while (textSpace(word) == False);
(array1)[i] = (char**)malloc(numAgdarot + 1 * sizeof(char*)); //set the num and agdarot
//save the word
(array1)[i][0] = (char*)malloc(strlen(word) * sizeof(char));
strcpy(array1[i][0], word);
//save the agdarot
for (int j = 1; j <= numAgdarot; j++)
{
printf("enter descrip number %d: ", i);
_flushall();
gets(descrip);
(array1)[i][j] = (char*)malloc(strlen(descrip) * sizeof(char));
strcpy(array1[i][j], descrip);
}
}
}
int main() {
int *sizeWords = NULL;
int size = 0;
char *x=NULL;// = "jk";
char *** array1 = NULL;
printf("enter number of word: ");
scanf("%d", &size);
array1 = (char***)malloc(size * sizeof(char**));
sizeWords = (int*)malloc(size * sizeof(int));
//x = temp(x,sizeWords);
//input the word and agdarot
input(array1, sizeWords, size);
for (int i = 0; i < size; i++)
{
for (int j = 0; j < sizeWords[i] + 1; j++)
{
free(array1[i][j]);
}
free(array1);
}
return 0;
}
I get a "HEAP CORRUPTION DELETED" error after Normal block. Why?
If i used a debugger I see the char * but i can not do a free..
Doing
malloc(strlen(word) * sizeof(char));
is almost always wrong. Remember that strings also contains an extra character that is not reported by the strlen function, the terminator character '\0'. That means your next call to strcpy will write beyond the end of the allocated memory.
What you should do is allocate memory for that extra terminator character as well:
array1[i][0] = malloc(strlen(word) + 1);
[Note that I changed the code, first because the parentheses around array are not needed, secondly because you in C one should not cast the return of malloc, and third because sizeof(char) is specified to always be 1.]
Remember to change on all other places where you use strlen in a call to malloc.
These allocations are too small:
(array1)[i][0] = (char*)malloc(strlen(word) * sizeof(char));
strcpy(array1[i][0], word);
// ...
(array1)[i][j] = (char*)malloc(strlen(descrip) * sizeof(char));
strcpy(array1[i][j], descrip);
You need an extra character for the terminating \0. strcpy() is writing into unallocated space.
Save yourself some trouble and:
(array1)[i][0] = strdup(word);
// ...
(array1)[i][j] = strdup(descrip);
And, as pointed out in the comments,
for (int i = 0; i < size; i++)
{
for (int j = 0; j < sizeWords[i] + 1; j++)
{
free(array1[i][j]);
}
free(array1);
}
should become:
for (int i = 0; i < size; i++)
{
for (int j = 0; j < sizeWords[i] + 1; j++)
{
free(array1[i][j]);
}
free(array1[i]);
}
free(array1);