Steven Watanabe skrev:

AMDG

strasser@uni-bremen.de wrote:

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Zitat von Thorsten Ottosen <nesotto@cs.aau.dk>:

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Hi John & co,

IIRC, std::copy() cannot use memcpy(), since the memory is allowed to overlap. Therefore it can only use memmove().

std::copy() doesn't allow overlapping ranges. -> std::copy_backward()

Both copy and copy_backwards allow some overlapping ranges.

int array[10] = {}; std::copy(&array[0], &array[7], &array[1]); // illegal std::copy(&array[1], &array[8], &array[0]); // okay std::copy_backwards(&array[0], &array[7], &array[8]); // okay std::copy_backwards(&array[1], &array[8], &array[7]); // illegal

Ok, so what is the conclusion? From the C standard: void *memcpy(void * restrict s1, const void * restrict s2, size_t n); Description [#2] The memcpy function copies n characters from the object pointed to by s2 into the object pointed to by s1. If copying takes place between objects that overlap, the behavior is undefined. I recall that STLPorts std::copy() used memmove(). How do we interpret "objects that overlap"? -Thorsten

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Hi John & co,

IIRC, std::copy() cannot use memcpy(), since the memory is allowed to overlap. Therefore it can only use memmove().

std::copy() doesn't allow overlapping ranges. -> std::copy_backward()

std::copy() does allow overlapping ranges. It requires the start of the range being copied to is not in the range from, but the end can be.

std::copy(it, it + 5, it - 1); is legal. The equivalent memcpy(it, it - 1, 5); is not

For exactly this reason, libstdc++ uses memmove rather than memcpy. memmove can also be used for copy_backward.

Updated examples and docs in Trunk, Thanks for catching this, John.