[英]std::unique_ptr with lambda custom deleter doesnt compile
在以下代码中找不到什么问题
std::unique_ptr<CFStringRef, std::function<void(CFStringRef)>>
cfstr(CFStringCreateWithCString(NULL, str, kCFStringEncodingUTF8),
[](CFStringRef obj){
CFRelease(obj);
});
CFStringCreateWithCString应该根据CFStringCreateWithCString文档返回正确的类型
错误:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -x c++ -arch x86_64 -fmessage-length=0 -fdiagnostics-show-note-include-stack -fmacro-backtrace-limit=0 -std=c++11 -stdlib=libc++ -Wno-trigraphs -fpascal-strings -O0 -Wno-missing-field-initializers -Wno-missing-prototypes -Wno-non-virtual-dtor -Wno-overloaded-virtual -Wno-exit-time-destructors -Wno-missing-braces -Wparentheses -Wswitch -Wno-unused-function -Wno-unused-label -Wno-unused-parameter -Wunused-variable -Wno-unused-value -Wno-empty-body -Wno-uninitialized -Wno-unknown-pragmas -Wno-shadow -Wno-four-char-constants -Wno-conversion -Wno-constant-conversion -Wno-int-conversion -Wno-bool-conversion -Wno-enum-conversion -Wno-shorten-64-to-32 -Wno-newline-eof -Wno-c++11-extensions -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk -fasm-blocks -fstrict-aliasing -Wdeprecated-declarations -Winvalid-offsetof -mmacosx-version-min=10.7 -g -fvisibility-inlines-hidden -Wno-sign-conversion -D_DEBUG -DDEBUG -MMD -MT dependencies -MF -c DynamicStore.cpp -o DynamicStore.o
DynamicStore.cpp:29:5: error: no matching constructor for initialization of 'std::unique_ptr<CFStringRef, std::function<void (CFStringRef)> >'
cfstr((CFStringRef)CFStringCreateWithCString(NULL, str, kCFStringEncodingUTF8),
main.cpp:73:14: note: in instantiation of function template specialization 'std::__1::for_each<std::__1::__wrap_iter<const std::__1::sub_match<const char *> *>, (lambda at main.cpp:73:45)>' requested here
std::for_each(cm.begin(), cm.end(), [](const std::cmatch &s){
^
main.cpp:73:45: note: candidate function not viable: no known conversion from 'const std::__1::sub_match<const char *>' to 'const std::cmatch' (aka 'const match_results<const char *>') for 1st argument
std::for_each(cm.begin(), cm.end(), [](const std::cmatch &s){
^
main.cpp:73:45: note: conversion candidate of type 'void (*)(const std::cmatch &)'
建立在@NulledPointer引用上:
struct CFStringRefDeleter {
using pointer = CFStringRef;
void operator()(CFStringRef ref) {
CFRelease(ref);
}
};
using CFStr_t = std::unique_ptr<CFStringRef, CFStringRefDeleter>;
CFStr_t cfstr(CFStringCreateWithCString(NULL, str, kCFStringEncodingUTF8));
CFStringRef obj = cfstr.get();
不确定是否足够,但是...如果我没记错的话,析构函数将使用指向该类型的指针,而不是该类型的对象
我的意思是...您应该将类型定义为
std::unique_ptr<CFStringRef, std::function<void(CFStringRef * )>>
^
note the pointer ---------------|
并且lambda应该接收(并使用)一个指针
[](CFStringRef * pObj){ CFRelease(*pObj) /* ? */ };
在max的答案中添加“为什么”部分:
根据unique_ptr文档
-Deleter必须是FunctionObject或对FunctionObject的左值引用或对函数的左值引用,可以使用类型为
unique_ptr<T, Deleter>::pointer
的参数进行调用
其中unique_ptr<T, Deleter>::pointer
解释了member types
如果存在该类型,则
unique_ptr<T, Deleter>::pointer
=std::remove_reference<Deleter>::type::pointer
,否则为T*
。 必须满足NullablePointer
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