如何在stringstream中放置一个字符串

Question

I have a vector:

vector<stringstream*> ssv;
for (int i = 0; i < cIter; i++) {
    ssv.push_back(new std::stringstream);
}

How can I put in elements of vector ssv strings?

I try:

string s1 = "easfef" + '\n';
int i = 0;
*ssv[i] << s1 << '\n';

But it give me an empty string:

string sdf = ssv[i]->str();

How can I do it?

Thanks for helping with '\\n', but it is stil a problem with vector: if i write:

std::string s1 = "qwerqwr\n";   // for example
int i = 0;
*ssv[i] << s1;

But give me an empty string as before

string sdf = ssv[i]->str();

Answer 1

Your main problem is how you initialize the string:

"easfef" + '\n'

The "easfef" decays into a const char * and '\\n' is promoted to an int with the value 10 (assuming ASCII). Then, the two are added together, which results in a pointer that points somewhere beyond your string literal. A crash is very possible, along with your mother being eaten by a dinosaur.

An easy way to fix this is to enforce std::string :

std::string s1 = std::string("easfef") + '\n';

An easier way is to inline the newline:

std::string s1 = "easfef\n";

Answer 2

In your code

string s1 = "easfef" + '\n';

the initialization expression will in practice compute as

"easfef" + 10;

which is a pointer to the eleventh character of the string.

But there is no such, so you have Undefined behavior .

---

Fix:

string s1 = string() + "easfef" + '\n';

---

That said, a vector of pointers to stringstream is almost certainbly an impractical solution to whatever problem you're trying to solve.

Try to describe the higher level problem.

Answer 3

In C++ string literals are raw arrays of chars , and arrays can be treated as pointers, and character literals like '\\n' can be treated as numbers, so "easfef" + '\\n' is interpreted as a pointer arithmetic operation.

You should write:

string s1 = "easfef";
s1 += '\n';