关于c_str()将strstream转换为sstream冲突 [英] Converting strstream to sstream conflict about c_str()

问题描述

我有这个用strstream编写的代码块.然后将其转换为sstream，如下所示.我不确定，但是我认为printStream->str()返回的是一个字符串对象，该对象带有printStream所指向的流缓冲区中的内容的副本(临时)，然后您在其上调用c_str()并得到一个const char *，然后放弃常量性，然后将指针返回到函数作用域之外.我认为由于您是从printStream->str()返回的临时值，因此将使用指针在该函数之外分配内存.我该怎么办?

I have this code block as written with strstream. And I converted it to sstream as below. I'm not sure, but I think printStream->str() is returning a string object with a copy (temporary) of the contents in the stream buffer pointed by printStream, and then then you are invoking c_str() on it and getting a const char *, and then casting away the const-ness, and then returning the pointer outside the function scope. I think since its a temporary value you are getting back from printStream->str(), you will be using a pointer to deallocated memory outside this function. How should I do this?

char * FieldData::to_string() const
{
  if(printStream)
    return printStream->str();
  FieldData* notConst = (FieldData*) this;
  notConst->printStream = new std::ostrstream;
  // check heap sr60315556
  if (notConst->printStream == NULL)
    return NULL;
  *(notConst->printStream) << "Invalid Field Type";
  *(notConst->printStream) << '\0';
  return printStream->str();
}

char * FieldData::to_string() const
{
  if(printStream)
    return const_cast<char *>(printStream->str().c_str());
  FieldData* notConst = (FieldData*) this;
  notConst->printStream = new std::ostringstream;
  // check heap sr60315556
  if (notConst->printStream == NULL)
    return NULL;
  *(notConst->printStream) << "Invalid Field Type";
  *(notConst->printStream) << '\0';
  return const_cast<char *>(printStream->str().c_str());
}

推荐答案

我认为一个叫做to_string的函数真的，真的， really 应该返回一个std::string.

I think a function called to_string really, really, really should return a std::string.

然后所有这些垃圾都可以替换为

And then all this junk can be replaced by

std::string FieldData::to_string() const
{ return "Invalid Field Type"; }

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