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Followup to close #1586

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hsutter
2020-03-26 11:43:27 -07:00
parent 6f01c706a8
commit 1ca5545ce1
1 changed files with 13 additions and 7 deletions
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CppCoreGuidelines.md
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@@ -20271,17 +20271,20 @@ and errors (when we didn't deal correctly with semi-constructed objects consiste
##### Example, bad ##### Example, bad
// Old conventional style: many problems
class Picture class Picture
{ {
int mx; int mx;
int my; int my;
char * data; char * data;
public: public:
// main problem: constructor does not fully construct
Picture(int x, int y) Picture(int x, int y)
{ {
mx = x, mx = x; // also bad: assignment in constructor body rather than in member initializer
my = y; my = y;
data = nullptr; data = nullptr; // also bad: constant initialization in constructor rather than in member initializer
} }
~Picture() ~Picture()
@@ -20289,6 +20292,7 @@ and errors (when we didn't deal correctly with semi-constructed objects consiste
Cleanup(); Cleanup();
} }
// bad: two-phase initialization
bool Init() bool Init()
{ {
// invariant checks // invariant checks
@@ -20298,10 +20302,11 @@ and errors (when we didn't deal correctly with semi-constructed objects consiste
if (data) { if (data) {
return false; return false;
} }
data = (char*) malloc(mx*my*sizeof(int)); data = (char*) malloc(mx*my*sizeof(int)); // also bad: owning raw * and malloc
return data != nullptr; return data != nullptr;
} }
// also bad: no reason to make cleanup a separate function
void Cleanup() void Cleanup()
{ {
if (data) free(data); if (data) free(data);
@@ -20320,11 +20325,11 @@ and errors (when we didn't deal correctly with semi-constructed objects consiste
class Picture class Picture
{ {
ptrdiff_t mx; int mx;
ptrdiff_t my; int my;
vector<char> data; vector<char> data;
static ptrdiff_t check_size(ptrdiff_t size) static int check_size(int size)
{ {
// invariant check // invariant check
Expects(size > 0); Expects(size > 0);
@@ -20333,7 +20338,7 @@ and errors (when we didn't deal correctly with semi-constructed objects consiste
public: public:
// even better would be a class for a 2D Size as one single parameter // even better would be a class for a 2D Size as one single parameter
Picture(ptrdiff_t x, ptrdiff_t y) Picture(int x, int y)
: mx(check_size(x)) : mx(check_size(x))
, my(check_size(y)) , my(check_size(y))
// now we know x and y have a valid size // now we know x and y have a valid size
@@ -20341,6 +20346,7 @@ and errors (when we didn't deal correctly with semi-constructed objects consiste
{ {
// picture is ready-to-use // picture is ready-to-use
} }
// compiler generated dtor does the job. (also see C.21) // compiler generated dtor does the job. (also see C.21)
}; };