How to add a variable value inside a text variable in C++

Question

In my C++ code, I am executing some commands using python as follows:

std::string word = "Something";
std::cout << word;                         //will execute using C++
PyRun_SimpleString("import sys");          // will execute using Python

The problem is how to pass word to Python ?

I want something like this: PyRun_SimpleString("Hello %" %word);

In Python you can do: "Hello {}".format(word) and the result "Hello Something"

I found something like this: sprintf(str, "hello %s", word); But the problem is printf or sprintf will send it to console and will not return the value of word.

Thank you. so can I use it in my example like this: new_word = sprintf(str, "Hello %s", word); ? — Lucas123
– Lucas123, Commented Apr 24, 2019 at 17:07
sprintf() returns the number of characters copied into str. You would need new_word = str; after sprintf() exits. But you really shouldn't be using sprintf() anyway. That is the C way of formatting strings. The C++ way is to use std::string::operator+ or a std::ostringstream instead — Remy Lebeau
– Remy Lebeau, Commented Apr 24, 2019 at 17:08

Remy Lebeau · Accepted Answer · 2019-04-24 17:17:05Z

3

In C++, you use the + operator to concatenate std::string objects.

PyRun_SimpleString() takes a const char* as input. std::string has a c_str() method for obtaining a const char* for the string.

So, you can do this:

std::string s = "Hello " + word;
PyRun_SimpleString(s.c_str());

Or simply this:

PyRun_SimpleString(("Hello " + word).c_str());

Alternatively, you can use a std::ostringstream instead to build up a formatted string:

std::ostringstream oss;
oss << "Hello " << word;
PyRun_SimpleString(oss.str().c_str());

edited Apr 24, 2019 at 17:17

answered Apr 24, 2019 at 17:05

Remy Lebeau

610k36 gold badges516 silver badges875 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Lucas123 Over a year ago

Thank you so much that is really helpful.

Aconcagua Over a year ago

Sidenote: There's no operator+ for numerical values (int, unsigned long, float, double, ...), only for character, C-strings and std::string. So if you need the former, you'd be using the std::ostringstream variant...

Collectives™ on Stack Overflow

How to add a variable value inside a text variable in C++

1 Answer 1

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related