通过QMap转换std :: transform

问题描述

我必须转换QMap 。我尝试使用std :: transform，因为它适用于QList，但编译失败。

#include <QCoreApplication>
#include <algorithm>
#include <QMap>

int main(int argc,char *argv[]) {
  QCoreApplication a(argc,argv);

  QMap<QString,int> map;
  map["one"] = 1;
  map["three"] = 3;
  map["seven"] = 7;

  QMap<QString,int> map2;

  std::transform(map.begin(),map.end(),std::back_inserter(map2),[](const QPair<QString,int>& item) {
      return qMakePair(item.first+"testing",item.second);
  });

  return a.exec();
}

在编译以上代码时出现以下错误。我想在不使用一般 for循环的情况下实现此目标，因为我的项目使用cppcheck并引发警告。

/usr/include/c++/7/bits/stl_iterator.h:490: error: no type named ‘value_type’ in ‘class QMap<QString,int>’
In file included from /usr/include/c++/7/bits/stl_algobase.h:67:0,from /usr/include/c++/7/algorithm:61,from ../../../../qt5.12.4/5.12.4/gcc_64/include/QtCore/qglobal.h:142,from ../../../../qt5.12.4/5.12.4/gcc_64/include/QtCore/qcoreapplication.h:43,from ../../../../qt5.12.4/5.12.4/gcc_64/include/QtCore/QCoreApplication:1,from ../test/main.cpp:1:
/usr/include/c++/7/bits/stl_iterator.h: In instantiation of ‘class std::back_insert_iterator<QMap<QString,int> >’:
../test/main.cpp:15:65:   required from here
/usr/include/c++/7/bits/stl_iterator.h:490:7: error: no type named ‘value_type’ in ‘class QMap<QString,int>’
       operator=(const typename _Container::value_type& __value)
       ^~~~~~~~

/usr/include/c++/7/bits/stl_algo.h:4306: error: no match for call to ‘(main(int,char**)::<lambda(const QPair<QString,int>&)>) (int&)’
In file included from /usr/include/c++/7/algorithm:62:0,from ../test/main.cpp:1:
/usr/include/c++/7/bits/stl_algo.h: In instantiation of ‘_OIter std::transform(_IIter,_IIter,_OIter,_UnaryOperation) [with _IIter = QMap<QString,int>::iterator; _OIter = std::back_insert_iterator<QMap<QString,int> >; _UnaryOperation = main(int,int>&)>]’:
../test/main.cpp:17:4:   required from here
/usr/include/c++/7/bits/stl_algo.h:4306:24: error: no match for call to ‘(main(int,int>&)>) (int&)’
  *__result = __unary_op(*__first);
              ~~~~~~~~~~^~~~~~~~~~
/usr/include/c++/7/bits/stl_algo.h:4306:24: note: candidate: QPair<QString,int> (*)(const QPair<QString,int>&) <conversion>
/usr/include/c++/7/bits/stl_algo.h:4306:24: note:   candidate expects 2 arguments,2 provided
../test/main.cpp:15:102: note: candidate: main(int,int>&)>
   std::transform(map.begin(),int>& item) {
                                                                                                      ^
../test/main.cpp:15:102: note:   no kNown conversion for argument 1 from ‘int’ to ‘const QPair<QString,int>&’

解决方法

一个主要问题是com.amazonaws.SdkClientException: Unable to load AWS credentials from any provider in the chain at com.amazonaws.auth.AWSCredentialsProviderChain.getCredentials(AWSCredentialsProviderChain.java:131) at com.amazonaws.http.AmazonHttpClient$RequestExecutor.getCredentialsFromContext(AmazonHttpClient.java:1119) at com.amazonaws.http.AmazonHttpClient$RequestExecutor.runBeforeRequestHandlers(AmazonHttpClient.java:759) at com.amazonaws.http.AmazonHttpClient$RequestExecutor.doExecute(AmazonHttpClient.java:723) at com.amazonaws.http.AmazonHttpClient$RequestExecutor.executeWithTimer(AmazonHttpClient.java:716) at com.amazonaws.http.AmazonHttpClient$RequestExecutor.execute(AmazonHttpClient.java:699) at com.amazonaws.http.AmazonHttpClient$RequestExecutor.access$500(AmazonHttpClient.java:667) at com.amazonaws.http.AmazonHttpClient$RequestExecutionBuilderImpl.execute(AmazonHttpClient.java:649) at com.amazonaws.http.AmazonHttpClient.execute(AmazonHttpClient.java:513) at com.amazonaws.services.s3.AmazonS3Client.invoke(AmazonS3Client.java:4221) at com.amazonaws.services.s3.AmazonS3Client.invoke(AmazonS3Client.java:4168) at com.amazonaws.services.s3.AmazonS3Client.invoke(AmazonS3Client.java:4162) at com.amazonaws.services.s3.AmazonS3Client.listObjectsV2(AmazonS3Client.java:861) at com.amazonaws.services.s3.AmazonS3Client.listObjectsV2(AmazonS3Client.java:833) at com.moveinsync.routeconfiguration.application.services.AmazonS3Abstraction.businessUnitExists(AmazonS3Abstraction.java:24) at com.moveinsync.routeconfiguration.application.services.AmazonS3Abstraction$$FastClassBySpringCGLIB$$a941c961.invoke(<generated>) at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218) at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:771) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163) at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:749) at org.springframework.cache.interceptor.CacheInterceptor.lambda$invoke$0(CacheInterceptor.java:53) at org.springframework.cache.interceptor.CacheAspectSupport.invokeOperation(CacheAspectSupport.java:366) at org.springframework.cache.interceptor.CacheAspectSupport.execute(CacheAspectSupport.java:421) at org.springframework.cache.interceptor.CacheAspectSupport.execute(CacheAspectSupport.java:346) at org.springframework.cache.interceptor.CacheInterceptor.invoke(CacheInterceptor.java:61) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:749) at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:691) at com.moveinsync.routeconfiguration.application.services.AmazonS3Abstraction$$EnhancerBySpringCGLIB$$a1dd8a75.businessUnitExists(<generated>) at com.moveinsync.routeconfiguration.application.services.RouteConfigurationServiceAmazonS3Impl.getRoutingParameters(RouteConfigurationServiceAmazonS3Impl.java:33) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:344) at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:198) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163) at org.springframework.cache.interceptor.CacheInterceptor.lambda$invoke$0(CacheInterceptor.java:53) at org.springframework.cache.interceptor.CacheAspectSupport.invokeOperation(CacheAspectSupport.java:366) at org.springframework.cache.interceptor.CacheAspectSupport.execute(CacheAspectSupport.java:421) at org.springframework.cache.interceptor.CacheAspectSupport.execute(CacheAspectSupport.java:346) at org.springframework.cache.interceptor.CacheInterceptor.invoke(CacheInterceptor.java:61) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:212) at com.sun.proxy.$Proxy78.getRoutingParameters(Unknown Source) at com.moveinsync.routeconfiguration.application.controllers.RouteConfigurationController.getConfiguration(RouteConfigurationController.java:20) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190) at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:105) at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:878) at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:792) at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040) at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943) at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) at javax.servlet.http.HttpServlet.service(HttpServlet.java:626) at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) at javax.servlet.http.HttpServlet.service(HttpServlet.java:733) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:143) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374) at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1590) at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Thread.java:748) 要呼叫std::back_inserter(map2)（也不是push_back的成员）QMap。

您还遇到一个问题，即标准插入程序希望在容器中定义std::map没有的value_type。在较早的版本中，QMap的含义不同于QMap::value_type。

您可以自己定义一个插入迭代器

std::map::value_type

直接替换#include <QCoreApplication> #include <algorithm> #include <QMap> template <typename K,typename T> struct QMapInsertIterator { QMap<K,T> & map; QMapInsertIterator& operator=(const QPair<K,T> & pair) { map.insert(pair.first,pair.second); return *this; } QMapInsertIterator& operator++() { return *this; } QMapInsertIterator& operator*() { return *this; } }; template <typename K,typename T> QMapInsertIterator<K,T> QMapInserter(QMap<K,T> & map) { return { map }; }

std::back_inserter