Difference between revisions of "cpp/algorithm/qsort"
| Line 34: | Line 34: | ||
int compare_ints(const void* a, const void* b) // comparison function | int compare_ints(const void* a, const void* b) // comparison function | ||
{ | { | ||
| − | register | + | register int arg1 = *reinterpret_cast<const int*>(a); |
| − | register | + | register int arg2 = *reinterpret_cast<const int*>(b); |
| − | + | if(arg1 < arg2) return -1; | |
| + | if(arg1 > arg2) return 1; | ||
| + | return 0; | ||
} | } | ||
Revision as of 13:56, 12 December 2012
Template:ddcl list begin <tr class="t-dsc-header">
<td><cstdlib>
<td></td> <td></td> </tr> <tr class="t-dcl ">
<td class="t-dcl-nopad">int (*comp)(const void *, const void *) );
<td class="t-dcl-nopad"> </td> <td class="t-dcl-nopad"> </td> </tr> Template:ddcl list end
Sorts the given array pointed to by ptr in ascending order. The array contains count elements of size size. Function pointed to by comp is used for object comparison.
Contents |
Parameters
| ptr | - | pointer to the array to sort |
| count | - | number of element in the array |
| size | - | size of each element in the array in bytes |
| comp | - | comparison function which returns a negative integer value if the first argument is less than the second, a positive integer value if the first argument is greater than the second and zero if the arguments are equivalent. The signature of the comparison function should be equivalent to the following: int cmp(const void *a, const void *b); The function must not modify the objects passed to it and must return consistent results when called for the same objects, regardless of their positions in the array. |
Return value
(none)
Notes
The type of the elements of the array must be a trivial type, otherwise the behavior is undefined.
Example
The following code sorts an array of integers using qsort().
#include <iostream> #include <cstdlib> int compare_ints(const void* a, const void* b) // comparison function { register int arg1 = *reinterpret_cast<const int*>(a); register int arg2 = *reinterpret_cast<const int*>(b); if(arg1 < arg2) return -1; if(arg1 > arg2) return 1; return 0; } int main() { int a[] = { -2, 99, 0, -743, 2, 3, 4 }; constexpr std::size_t size = sizeof(a)/sizeof(int); std::qsort(a, size, sizeof(int), compare_ints); for (int ai : a) std::cout << ai << ' '; }
Output:
-743 -2 0 2 3 4 99
See also
| (C++11) |
checks if a type is trivial (class template) |
| C documentation for qsort
| |
