Question

I have a single buffer, and several pointers into it. I want to sort the pointers based upon the bytes in the buffer they point at.

qsort() and stl::sort() can be given custom comparision functions. For example, if the buffer was zero-terminated I could use strcmp:

int my_strcmp(const void* a,const void* b) {   const char* const one = *(const char**)a,   const two = *(const char**)b;   return ::strcmp(one,two); } 

however, if the buffer is not zero-terminated, I have to use memcmp() which requires a length parameter.

Is there a tidy, efficient way to get the length of the buffer into my comparision function without a global variable?

Answer 1

Is there a reason you can’t null-terminate your buffers?

If not, since you’re using C++ you can write your own function object:

 struct MyStrCmp {     MyStrCmp (int n): length(n) { }     inline bool operator< (char *lhs, char *rhs) {        return ::strcmp (lhs, rhs, length);     }     int length;  };  // ...  std::sort (myList.begin (), myList.end (), MyStrCmp (STR_LENGTH));