添加字符串时遇到问题......（c ++）

Question

For some reason my source file will not compile because of my toString function. It claims it cannot recognize the + symbol to append strings. Here's my code:

string s = "{symbol = " + symbol + ", qty = " + qty + ", price = " + price + "}";

symbol, qty, and price are variables in the class

I get the following message from the compiler...

CLEAN SUCCESSFUL (total time: 55ms)

mkdir -p build/Debug/GNU-MacOSX
rm -f build/Debug/GNU-MacOSX/Stock.o.d
g++    -c -g -MMD -MP -MF build/Debug/GNU-MacOSX/Stock.o.d -o build/Debug/GNU-MacOSX/Stock.o Stock.cpp
Stock.cpp: In member function 'std::string Stock::toString()':
Stock.cpp:56: error: no match for 'operator+' in 'std::operator+(const std::basic_string<_CharT, _Traits, _Alloc>&, const _CharT*) [with _CharT = char, _Traits = std::char_traits<char>, _Alloc = std::allocator<char>](((const char*)", qty = ")) + ((Stock*)this)->Stock::qty'
make: *** [build/Debug/GNU-MacOSX/Stock.o] Error 1


BUILD FAILED (exit value 2, total time: 261ms)

Anyone know what's going on here?

Answer 1

You can't call std::string::operator+ on int types, use std::stringstream

#include <sstream>
#include <string>

std::stringstream ss;
ss << "{symbol = " << symbol << ", qty = " << qty << ", price = " << price << "}";

std::string s = ss.str();

Or use std::to_string if you use C++11 and boost::lexical_cast to cast integer types to string first:

std::string s = "{symbol = " + symbol + ", qty = " + std::to_string(qty) 
                + ", price = " + std::to_string(price) + "}";

Answer 2

If qty and price are ints or something similar you can do the following (in C++11):

string s = "{symbol = " + symbol + ", qty = " + std::to_string(qty) + ", price = " + std::to_string(price) + "}";

example