C++: insert char to a string

问题:

so I am trying to insert the character, which i got from a string, to another string. Here I my actions: 1. I want to use simple:

someString.insert(somePosition, myChar);

2. I got an error, because insert requires(in my case) char* or string
3. I am converting char to char* via stringstream:

stringstream conversion;
char* myCharInsert;
conversion << myChar //That is actually someAnotherString.at(someOtherPosition) if that matters;
conversion >> myCharInsert;
someString.insert(somePosition, myCharInsert);

4. Everything seems to be compiling successfully, but program crashes the gets to

conversion >> myCharInsert;

line.

5.I am trying to replace char* with string:

stringstream conversion;
char* myCharInsert;
conversion << myChar //That is actually someAnotherString.at(someOtherPosition) if that matters;
conversion >> myCharInsert;
someString.insert(somePosition, myCharInsert);

Everything seems to be OK, but when someAnotherString.at(someOtherPosition) becomes space, program crashes.

So how do I correctly do this?

回答1:

There are a number of overloads of std::string::insert. The overload for inserting a single character actually has three parameters:

string& insert(size_type pos, size_type n, char c);

The second parameter, n, is the number of times to insert c into the string at position pos (i.e., the number of times to repeat the character. If you only want to insert one instance of the character, simply pass it one, e.g.,

someString.insert(somePosition, 1, myChar);

回答2:

Simplest is to provide yourself with a function that turns a character into a string. There are lots of ways of doing this, such as

string ToStr( char c ) {
   return string( 1, c );
}

Then you can simply say:

someString.insert(somePosition, ToStr(myChar) );

and use the function in other cases where you want a string but have a char.

回答3:

4. Everything seems to be compiling successfully, but program crashes the gets to

conversion >> myCharInsert;

The problem is that you are trying to dereference(access) myCharInsert(declared as a char* ) which is pointing to a random location in memory(which might not be inside the user's address space) and doing so is Undefined Behavior (crash on most implementations).

EDIT

To insert a char into a string use string& insert ( size_t pos1, size_t n, char c ); overload.

Extra

To convert char into a std::string read this answer