I have this pointer to char with a collection of c-strings
d|o|g|\0|g|h|o|s|t|\0|r|e|a|p|e|r|\0
I am using qsort() method from c library O want to sort it ascending order
but I am comfused on how to short this by string not by char.
I have a char pointer that points to the start of the orginal pointer but what i need is to sort the original char pointer not the new char* and still sort the new char*. without having dangling pointers
You need to create an array of char* to the start of each string in the original array. then you can sort the new array of char* by whatever sorting function you need.
Here is a sample of what this would look like.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
size_t multi_string_count(char* str) {
size_t count = 0;
while(*str) {
++count;
str += strlen(str) + 1;
}
return count;
}
char** split_multi_string(char* str, size_t* numberOfStrings) {
size_t i;
char** strArray;
*numberOfStrings = multi_string_count(str);
// allocate a new block of memory to hold the array
strArray = (char**)malloc(*numberOfStrings * sizeof(char*));
for(i=0; i < *numberOfStrings; ++i) {
// store the starting address of the string into the array
strArray[i] = str;
str += strlen(str) + 1;
}
return strArray;
}
int my_comp (const void* p1, const void* p2) {
return strcmp((const char*)p1, (const char*)p2);
}
int main(int argc, char* argv[]) {
size_t i, arrayLength;
char** strArray;
char* multiStr = "dog\0ghost\0reaper\0cat\0";
strArray = split_multi_string(multiStr, &arrayLength);
// Sort the array of pointers by the comparitor function
qsort(strArray, arrayLength, sizeof(char*), my_comp);
for(i=0; i < arrayLength; ++i)
printf("%s, ", strArray[i]);
free(strArray); // Free up the dynamically allocated array.
return 0;
}
qsort() can't do that, and it's not obvious to me how you'd do it even with your own algorithm.
I think this what you are looking for.
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int stringCompare(const void* p1, const void* p2)
{
char** lhs = (char**)p1;
char** rhs = (char**)p2;
return strcmp(*lhs, *rhs);
}
int main()
{
char s1[] = {'d', 'o', 'g', '\0', 'g', 'h', 'o', 's', 't', '\0', 'r', 'e', 'a', 'p', 'e', 'r', '\0'};
char* s2[] = {s1, s1+4, s1+10};
qsort(s2, 3, sizeof(char*), stringCompare);
printf("%s\n", s2[0]);
printf("%s\n", s2[1]);
printf("%s\n", s2[2]);
};
stringCompare. Couldn't you just pass strcmp directly to qsort?iostream?strcmp directly because it uses char* and qsort needs void*. Blech.
Below is a sample program which you can refer to
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int compare (const char* a, const char* b)
{
return strcmp(a, b);
}
int main(void) {
char *ar[3] = {"dog", "cat", "pig"};
int i;
qsort(ar, 3, sizeof(char*), compare); // here 3 is the number of elements in array
printf("Data after sorting\n");
for(i=0; i<3; i++)
printf("%s\n", ar[i]);
return 0;
}
Here i have initialized the array during declaration, but you can initialize it later also.
sizeof (char *) rather than 4