C++禁止从const char*设置char*和char []

Question

这是代码.我不知道它为什么不承认它需要复制内存,我不能强迫它.

 string message="The quick brown fox jumped over the lazy dog.";

  vector<char*> words;

  while(message.length()>0){
    char wtf[message.substr(0,message.find(" ")).c_str().length()]=message.substr(0,message.find(" ")).c_str();
    words.push_back(wtf);
    message=message.substr(message.find(" ")+1);
  }

我看到有类似的线程,但没有.而且,C++似乎无法轻易解决这个问题.

Answer 1

您希望按空格将字符串拆分为标记.你应该使用一个合适的工具 - 例如Boost.Tokenizer.您的代码在几个方面有误:

1. 您无法定义这样的数组,维度必须是编译时常量表达式.
2. 数组不是指针,也不能分配给数组.
3. c_str 只要字符串对象有效,就返回一个有效的指针.
4. char*除非你需要,否则不要使用.使该向量保持不变std::string.
5. c_str返回一个char*没有length成员函数的函数,或者该函数的任何成员函数.

这表明你在C++中缺乏一些基本的知识.你应该读一本关于C++的好书.所以,不,这不是C++的缺点.

真的,只需使用Boost.Tokenizer.它有一个按文档中的空格分割的示例.

Answer 2

如何将文本分解为单词(简单方法)

#include <string>
#include <sstream>
#include <vector>
#include <algorithm>
#include <iterator>

int main()
{
    std::string message="The quick brown fox jumped over the lazy dog.";

    std::vector<std::string>    words;

    std::stringstream   stream(message);                  // 1: Create a stream
    std::copy(std::istream_iterator<std::string>(stream), // 2: Copy words from the stream
              std::istream_iterator<std::string>(),
              std::back_inserter(words));                 //    into the back of the vector.
}

分解它是如何工作的(对于12岁的学习计划)

• 运算符>>应用于流(和字符串)时读取单个(白色)空格分隔的单词.

  std::string message="The quick brown fox jumped over the lazy dog.";
  std::stringstream   stream(message);
  
  std::string  word;
  stream >> word; // Reads "The"
  stream >> word; // Reads "quick"
  stream >> word; // Reads "brown" etc...
  

• istream_iterator是流的适配器,使它们看起来像容器.
  它使用运算符>>从"T"类型的流中读取项目

  std::stringstream   stream("The quick brown fox jumped over the lazy dog.");
  std::istream_iterator<std::string> i(stream);
  
  std::string  word;
  
  word = *i;      // de-reference the iterator to get the object.   Reads "The"
  ++i;
  word = *i; ++i; // Reads "quick"
  word = *i; ++i; // Reads "brown" etc
  
  // Works for any type that uses >> to read from the stream 
  std::stringstream   intstream("99 40 32 64 20 10 9 8 102");
  std::istream_iterator<int> i(stream);  // Notice the type is int here
  
  int   number;
  
  number = *i;      // de-reference the iterator to get the object.   Reads "99"
  ++i;
  number = *i; ++i; // Reads "44"
  number = *i; ++i; // Reads "32" etc
  

• 标准算法都适用于迭代器.
  std :: copy遍历源并将每个项目放在目标中:

  int    src[] = { 1, 2, 3, 4, 5, 6 };
  int    dst[] = { 0, 0, 0, 0, 0, 0 };
  
  std::copy(src, src+6, dst); // copies src into dst
                              // It assumes there is enough space in dst
  

• back_inserter是一个使用push_back将项添加到容器的适配器.
  我们可以确保目标向量的大小正确.但是使用back_inserter更容易确保向量是动态调整大小的.

  int    src[] = { 1, 2, 3, 4, 5, 6 };
  std::vector<int> dst; // Currently has zero size
  
  std::copy(src, src+6, std::back_inserter(dst)); // copies src into dst
                                                  // back_inserter expands dst to fit
                                                  // by using push_back
  

• 将它们重新组合在一起:

  // Create a stream from the string
  std::stringstream   stream(message);
  
  // Use std::copy to copy from the string.
  //     The stream is iterated over a word at a time.
  //     because the istream iterator is using std::string type.
  //
  //     The istream_iterator with no parameters is equivelent to end.
  //
  //     The destination appends the word to the vector words.
  std::copy(std::istream_iterator<std::string>(stream), // 2: Copy words from the stream
            std::istream_iterator<std::string>(),
            std::back_inserter(words));                 //    into the back of the vector.