Difference between revisions of "cpp/string/byte/memcmp"
From cppreference.com
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===Notes=== | ===Notes=== | ||
| − | This function reads object representations, not the object values, and is typically meaningful for trivially-copyable objects only. For example, {{tt|memcmp()}} between two objects of type {{lc|std::string}} or {{lc|std::vector}} will not compare their contents. | + | This function reads [[cpp/language/object|object representations]], not the object values, and is typically meaningful for trivially-copyable objects only. For example, {{tt|memcmp()}} between two objects of type {{lc|std::string}} or {{lc|std::vector}} will not compare their contents. |
===Example=== | ===Example=== | ||
Revision as of 07:30, 27 January 2014
| Defined in header <cstring>
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| int memcmp( const void* lhs, const void* rhs, std::size_t count ); |
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Reinterprets the objects pointed to by lhs and rhs as arrays of unsigned char and compares the first count characters of these arrays. The comparison is done lexicographically.
Contents |
Parameters
| lhs, rhs | - | pointers to the memory buffers to compare |
| count | - | number of bytes to examine |
Return value
Negative value if the first differing byte (reinterpreted as unsigned char) in lhs is less than the corresponding byte in rhs.
0 if all count bytes of lhs and rhs are equal.
Positive value if the first differing byte in lhs is greater than the corresponding byte in rhs.
Notes
This function reads object representations, not the object values, and is typically meaningful for trivially-copyable objects only. For example, memcmp() between two objects of type std::string or std::vector will not compare their contents.
Example
Run this code
#include <iostream> #include <cstring> int main() { char a1[] = {'a', 'b', 'c'}; char a2[] = {'a', 'b', 'd'}; std::cout << "'abc' vs 'abd': " << std::memcmp(a1, a2, sizeof a1) << '\n' << "'abd' vs 'abc': " << std::memcmp(a2, a1, sizeof a1) << '\n' << "'abc' vs 'abc': " << std::memcmp(a1, a1, sizeof a1) << '\n'; }
Output:
'abc' vs 'abd': -1 'abd' vs 'abc': 1 'abc' vs 'abc': 0
See also
| compares two strings (function) | |
| compares a certain number of characters from two strings (function) | |
| C documentation for memcmp
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