Xcode STL C Debug编译错误

码：

#include <iostream>
#include <String>
#include <fstream>
#include <sstream>

using namespace std;

int main (int argc,char * const argv[]) {
    String cppfilename; 
    std::cout << "Please enter the filename to create: ";

    while ( cppfilename == "" ) {
        getline(cin,cppfileName);    // error occurs here
    }

    cppfilename += ".txt";
    ofstream fiLeout;
    fiLeout.open( cppfilename.c_str() );
    fiLeout << "WriTing this to a file.\n"; 
    fiLeout.close();

    return 0;
}

调试输出：

Please enter the filename to create: Running…
myfile
FileIO(5403) malloc: *** error for object 0xb3e8: pointer being freed was not allocated
*** set a breakpoint in malloc_error_break to debug
Created: myfile.txt

发布输出：

FileIO implementation C++
Please enter the filename to create: Running…
myfile
Created: myfile.txt

除了没有检查文件描述符是否打开(为简单起见)这个代码有什么问题？

更新：我将代码分解为以下内容,但仍然存在错误：

String cppfilename; 
 getline(cin,cppfileName);    // error here