Create function which sorts 2 given sorted strings - c

Question

Given two sorted strings, I need to merge these strings to one string, and make it sorted.
sort by the ASCII value. for example:
acdty, berz => abcdertyz
My code:
#include <stdio.h>
#include <stdlib.h>
char* PairSortedArrays(char a[], char b[]) {
char* c = (char*)malloc((sizeof(a) + sizeof(b)) * sizeof(char));
int i, aPos = 0, bPos = 0;
for (i = 0; i < sizeof(*c); i++) {
if ((int)(a[aPos]) <= (int)(b[bPos])) {
c[i] = a[aPos];
aPos++;
}
else {
c[i] = b[bPos];
bPos++;
}
}
return c;
}
int main()
{
printf("%s", PairSortedArrays("acdty", "berz"));
return 0;
}
The first problem is with sizeof(a). if I code: printf("%d", sizeof(a)); it prints 8, while I expect it to print 5.

Answer 1

The expression i < sizeof(*c) controling the for loop is the main culprit. The corrected version of your program could be: (I edited the code a bit)
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
char* PairSortedArrays(const char a[], const char b[])
{
size_t i;
const size_t total_len = strlen(a)+strlen(b);
char *c = malloc(total_len + 1);
size_t aPos = 0, bPos = 0;
for (i = 0; i < total_len; i++) {
if (a[aPos] == '\0') {
strcpy(c + i, b + bPos);
break;
}
if (b[bPos] == '\0') {
strcpy(c + i, a + aPos);
break;
}
c[i] = a[aPos] < b[bPos] ? a[aPos++] : b[bPos++];
}
return c;
}
int main()
{
printf("%s\n", PairSortedArrays("acdty", "berz"));
printf("%s\n", PairSortedArrays("az", "ks"));
return 0;
}
The return value of malloc must be checked against NULL in a real program. Also there is a memory leak (easy to fix).

Answer 2

When working with strings in C, you will want to be using strlen() to see how long they are, not sizeof (which merely tells you what the size of a pointer is).
Also note that sizeof(char) is 1 by definition, so there's no need to say "* sizeof(char)" in your malloc

Answer 3

sizeof(a) will return the size of a pointer in this case which will be 8 bytes if you compile for 64 architecture.
you have to either pass the size of each string or loop the string characters until you reach the '\0' if the string is null-terminated.

Answer 4

You should consider using qsort:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int compare_chars(const void *p1, const void *p2)
{
return *(const char *)p1 - *(const char *)p2;
}
char *PairSortedArrays(char *a, char *b)
{
char *c = malloc(strlen(a)+strlen(b)+1);
strcpy(c, a);
strcat(c, b);
qsort(c, strlen(c), sizeof(char), compare_chars);
return c;
}
int main()
{
printf("%s", PairSortedArrays("acdty", "berz"));
return 0;
}