I want to read a set of strings in an array. The size of the array is to be decided at run-time using malloc or alloc i.e. the number of strings are accepted as input. I tried the following code but it doesn't worked.
char *array;
array=(char*)malloc(sizeof(char)*t); //t is the size of array
for(int temp=0;temp<t;temp++)
{
gets(a[temp]);
}
The same worked in case of array of integers.
Please help me in finding the solution.
C doesn't have any automatic built-in support for storing strings, there is no variable that is "a string", and can automatically grow to hold the proper number of characters. You need to allocate the memory yourself.
What you're doing now, is allocating place for the proper number of character pointers, but not for any characters. So the gets() call is writing into memory that is not allocated, which is undefined behavior. Since the integers fit completely in a single allocation each, that's why similar code worked for integers. Strings are more complex, so you need to do more work.
If there is any known upper bound on the length of these strings, you can use a temporary buffer of fixed length, and then copy from that into newly allocated dynamic memory once you know the required size. If there is no such bound, you need to repeat the same concept, by reading a fixed block, storing that, and if no end of line was found, read another block, grow the memory allocation for this string using realloc(), append the new characters, and repeat until the line ends.
As a side note, you should always avoid using gets(), since it doesn't support protecting your program against buffer overrun. It's much better to use fgets(), documented on the same page.
What you allocate is space for exactly one string, stored in zero-terminated format.
If you want to store an array of several strings, you need to malloc() an array of char * PLUS the several strings.
Besides, gets() is unsafe, as there is no size limit. Instead, use fgets(). It has the following signature:
char *fgets(char *restrict s, int n, FILE *restrict stream);
As it wants a stream, you just should give stdin.
So the best way to read one line is
char * read_one_line(uint32_t maxbufsize)
{
char * s = malloc(maxbufsize);
if (!fgets(s, maxbufsize, stdin)) {
free(s);
return NULL;
} else {
char * s2 = realloc(s, strlen(s)+1); // +1 for the NUL at the end
if (s2) {
return s2;
} else {
return s; // should never happen as the memory block is shrinked
}
}
}
This function allocates the memory needed for one line, resizes it appropriately after reading and leaves it to the caller to free it again at the appropriate time.
You need to allocate space for an array of strings (char*) first:
char **array;
array = (char**)malloc(sizeof(char*)*t);
Then you need to allocate space for each of them (let's 50 to be maximum count of characters for these strings):
int i = 0, m = 50;
for (i = 0; i < t; ++i)
array[i] = (char*)malloc(sizeof(char)*51); // 51 = 50 characters + '\0'
And then you can do what you wanted to do:
for(i = 0; i < t; ++i)
scanf("%50s", array[i]);
Instead of gets, it's better to use scanf with specified width (%50s = 50 characters + '\0').
Just remember that at-last in character array there should be a NUL character.
so allocate t+1 bytes of memory with alloc or malloc.
t bytes for the characters and 1 byte for the terminating NUL character.
after your for loop, i.e. outside of the loop, just write
a[temp] = '\0';
then you can take it in work.
I hope it will work.
it will look like this
char *a = malloc(sizeof((char)*(t+1)));//t is number if characters
int temp;
for(temp=0; temp<t; temp++) {
gets(a[temp]);
}
a[temp] = 0;
then print array and you'll get a string.
printf("%s",a);
malloc for every character?!
gets(). Not good.
malloc(t)? :-)