“无可行转化”与柠檬为ang,但有效的g ++ [英] "no viable conversion" with lemon for clang but valid for g++
问题描述
目前,我尝试在我们的项目中加入柠檬图书馆。
大多数开发人员在Windows上,他们使用MSVC编译,但我负责(这部分)使用gcc和clang进行编译。
Currently, I try to incorporate lemon library in our project. Most developers are on Windows, they compile with MSVC, but I am in charge (for this part) to compile with gcc and clang.
gcc不能重现的错误,我设法减少代码:
I came across an error with clang that gcc does not reproduce and I managed to reduce the code:
#include <lemon/dfs.h>
int main() {
lemon::ListDigraph g{};
lemon::ListDigraph::Node node = g.nodeFromId(42);
lemon::Dfs<lemon::ListDigraph> dfs{g};
lemon::SimplePath<lemon::ListDigraph> path = dfs.path(node);
return 0;
}
使用gcc,没有错误。
With gcc, no errors.
/usr/bin/g++-5 -std=c++11 -Wall -O3 -I${SRC_ROOT}/external/lemon/latest -I${BIN_ROOT}/lemon -o ${TMP_ROOT}/core/src/core.cpp.o -c ${SRC_ROOT}/core/src/core.cpp
但是用clang:
/usr/bin/clang++-3.7 -std=c++11 -Wall -stdlib=libc++ -O3 -I${SRC_ROOT}/external/lemon/latest -I${BIN_ROOT}/lemon -o ${TMP_ROOT}/core/src/core.cpp.o -c ${SRC_ROOT}/core/src/core.cpp
In file included from ${SRC_ROOT}/core/src/core.cpp:1:
In file included from ${SRC_ROOT}/external/lemon/latest/lemon/dfs.h:31:
${SRC_ROOT}/external/lemon/latest/lemon/path.h:408:23: error: no viable
conversion from 'typename PredMapPath<ListDigraph, NodeMap<Arc> >::RevArcIt' to
'lemon::ListDigraphBase::Arc'
data[index] = it;;
^~
注意:
-
SRC_ROOT
,BIN_ROOT
,TMP_ROOT
被替换为可读性 - 代码片段不会工作,但应该编译(我将更正真正的大代码)
- 我真的需要真正的源代码的c ++ 11功能。
-
gcc
li>
-
clang
3.7 -
.1
SRC_ROOT
,BIN_ROOT
,TMP_ROOT
are replaced for readability- the snippet source code won't work, but should compile (I will correct the real big code)
- I really need the c++11 features for the real source code.
gcc
5clang
3.7lemon
1.3.1
问题:
- $
- 如何解决这个错误?
- Did I forget to clang a flag?
- Does lemon is fully compatible with clang?
- How to solve this error?
推荐答案
这是一个 double dispatch 相关问题
中的代码 http://lemon.cs.elte.hu/hg/lemon/file/9fd86ec2cb81/lemon /path.h#l443
template <typename CPath>
void buildRev(const CPath& path) {
int len = path.length();
data.resize(len);
int index = len;
for (typename CPath::RevArcIt it(path); it != INVALID; ++it) {
--index;
data[index] = it;; // sic!
}
}
依赖于此用户定义的 cast-operator
http:// lemon .cs.elte.hu / hg / lemon / file / 9fd86ec2cb81 / lemon / bits / path_dump.h#l139
operator const typename Digraph::Arc() const {
return path->predMatrixMap(path->source, current);
}
但分配表达式的左手类型
but the left hand type of the assigment expression
http:/ /lemon.cs.elte.hu/hg/lemon/file/9fd86ec2cb81/lemon/list_graph.h#l89
class Arc {
friend class ListDigraphBase;
friend class ListDigraph;
protected:
int id;
explicit Arc(int pid) { id = pid;}
public:
Arc() {}
Arc (Invalid) { id = -1; }
bool operator==(const Arc& arc) const {return id == arc.id;}
bool operator!=(const Arc& arc) const {return id != arc.id;}
bool operator<(const Arc& arc) const {return id < arc.id;}
};
没有自定义赋值运算符,但是clang尝试匹配的单参数自定义ctor对右侧的转换。
doesn't have a custom assignment operator, but a single-argument custom ctor that clang tries to match against conversions of the right side. And fails.
修改上述右侧的 lemon / path.h,第#443行
with a simple explicit cast operator invocation
Patching the right side of above shown lemon/path.h, line #443
with an simple explicit cast operator invocation
data[index] = it.operator const typename Digraph::Arc();;
使代码至少用clang(3.5)编译。
makes the code at least compile with clang (3.5).
柠檬 - 开发者必须决定这是否是期望的行为;应为此提交错误报告。
The lemon-developers must decide whether this is desired behavior; a bug report should be filed for this.
这篇关于“无可行转化”与柠檬为ang,但有效的g ++的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!