Is bounds checking in C or C++ expensive? -

Is bounds checking in C or C++ expensive? -

bound checking expensive (> x2 times runtime overhead)

i got point above 1 of professors. confused that. know, time-consuming part of programme io(from network , hard disks).

but bounds checking in c or c++ not related 2 input sources. example, re-create content of 1 buff in c using memcpy(dest, src, length(src)). before that, check size of src in order prevent heap overflow. precess can image is: start-address of src , \x00 byte in src(in view of assembly language, re-create content of src 1 1 , see if byte equivalent \x00). after getting 2 address, substract them length of src. read content of src memory. know reading things memory fast.

i ran programme had iterator bounds checking turned on.

the running time went 789 ms 2608 ms.

so yes, can matter. not time, more never.

in particular, bound-checked iterators require @ to the lowest degree twice much storage simple pointers, , furthermore, not optimized. in theory they're simple , efficient, in practice don't want work don't need to.

oh, , did mention compile time went 7.72 seconds 13.21 seconds well?

for many nonbelievers among you... miniature illustration takes 0.92 seconds without bounds checking , 1.96 seconds with.

since there's lot of skepticism everything, including vector's efficiency... here's one:

#include <cstdio> #include <ctime> template<class t> struct vector { t *b, *e; vector(size_t n) : b(new t[n]), e(b + n) { } t &operator[](size_t i) { homecoming b[i]; } t &at(size_t i) { if (i >= e - b) { throw "invalid"; } homecoming b[i]; } }; #define @ operator[] // comment out enable bounds-checking int main(int argc, char **argv) { vector<size_t> v(1 << 16); (size_t *p = v.b; p != v.e; ++p) { *p = 1; } clock_t begin = clock(); (int j = 0; j < 1 << 12; ++j) { (size_t = 8, n = v.e - v.b; < n; ++i) { v.at(i) += v.at(i - 8); v.at(i) ^= v.at(i - 7); v.at(i) -= v.at(i - 6); v.at(i) ^= v.at(i - 5); v.at(i) += v.at(i - 4); v.at(i) ^= v.at(i - 3); v.at(i) -= v.at(i - 2); v.at(i) ^= v.at(i - 1); } } clock_t end = clock(); fprintf(stderr, "%u\n", clock() - begin); } 2.09 seconds vs. 0.88 seconds.

c++ c