Question

我在Sol.h中有以下代码，大多数由于学校规则而被忽略：

template <typename T,int promote = 1, typename compare = std::less<T>() >
class Sol{
private:
  struct node{
    T data;
    struct node *next;
    struct node *previous;
  };
node *head, *tail;
public:
  typedef unsigned int size_type;
  typedef T key_type;
  typedef T value_type;
  size_type count;
  Sol() : head(0), tail(0) {
    count=0;
  }

基本上它是一个类似于vector的容器，但它做了一些我们需要模板化的东西。我似乎无法得到“typename compare = std :: less＆lt; T＆gt;” - 留出空间。

当我使用测试代码编译时，我从Sol.h中得到两个错误，其余的都与它们有关。

>temple> g++ -Wall -Wextra -ansi -pedantic Sol.h main.cc
Sol.h:6:61: error: expected type-specifier
Sol.h:6:61: error: expected '>'
main.cc: In function 'int main()':
main.cc:19:19: error: template argument 3 is invalid
main.cc:19:24: error: invalid type in declaration before '(' token
main.cc:19:48: error: expression list treated as compound expression in initializer [-fpermissive]
main.cc:19:48: warning: left operand of comma operator has no effect [-Wunused-value]
main.cc:19:48: error: invalid conversion from 'char*' to 'int' [-fpermissive]
main.cc:20:19: error: template argument 3 is invalid
main.cc:20:31: error: expected initializer before 'it'
main.cc:22:13: error: request for member 'erase' in 'foo', which is of non-class type 'int'
main.cc:24:9: error: 'it' was not declared in this scope
main.cc:24:18: error: request for member 'find' in 'foo', which is of non-class type 'int'
main.cc:25:9: error: request for member 'end' in 'foo', which is of non-class type 'int'
main.cc:28:13: error: request for member 'find' in 'foo', which is of non-class type 'int'
main.cc:30:13: error: request for member 'find' in 'foo', which is of non-class type 'int'
main.cc: In function 'std::string cat(const T&) [with T = int, std::string = std::basic_string<char>]':
main.cc:23:24:   instantiated from here
main.cc:12:35: error: 'int' is not a class, struct, or union type
main.cc:12:50: error: request for member 'end' in 'con', which is of non-class type 'const int'
main.cc:12:35: error: 'int' is not a class, struct, or union type
main.cc:12:35: error: 'int' is not a class, struct, or union type
main.cc:12:35: error: 'int' is not a class, struct, or union type

要清楚，第6行是模板行。

Answer 1

更改

typename compare = std::less<T>()

要

typename compare = std::less<T>

你想要一个类型，而不是一个对象。

此外，您必须执行#include <functional>，因为这是定义std::less的位置。

如何将std :: less <t>作为类型名导入？</t>

1 个答案: