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How to convert? C-string format of toString() [closed]

stackoverflow.com › questions › 35569195 › how-to-convert-c-string-format-of-tostring

need a c-string format of toString()

If you just need to convert the output of toString(), you can use

const char* s = toString().c_str();

Note that c_str simply returns a pointer to the underlying character storage of the string. So you do need to be careful to not get a pointer to the string and then having that string go out of scope, in which case the pointer may or may not still point to valid memory. Your function currently is returning a string (I'm guessing your code has using namespace std) which means a C++ string object.

If you don't absolutely need C strings, I would recommend using C++ strings, since they are more current and just easier to work with. However, if for reasons somewhere else in the code you do need a C string, your function should look like

char* toString() {
    // formatting your output
}

Because all a C string is is a null terminated ('\0') array of char, and an array is equivalent to a pointer to the first element, so that's where char* comes from.

Because of that, something needs to “own” the memory of that character array, and that something needs to have a “lifetime” that is at least as long as the scope you need it for. If you make a function that returns a raw char * you should make sure that the pointer is to either a:

static string literal
a dynamically allocated string with the new operator that you then make sure to delete later.

In either case, C++ stringstreams could make formatting your output far more intuitive. You will need #include <sstream> and then some googling will steer you in the right direction. This solution also works if you need a C string, because C++ strings have a method called c_str() that converts C++ strings into C strings (null terminated array of characters):

#include <string>
#include <sstream>
using namespace std;

string toString() {
    stringstream ss; // these are so useful!
    if (*d != 1) {
        // this probably isn't the exact formatting you are looking for,
        // but stringstreams can certainly do it if you research a bit!
        ss << *n << *d;
    }
    else {
        ss << *n;
    }
    return ss.str();
}

void function_that_needs_c_string(const char * c);

int main() {
    function_that_needs_c_string(toString().c_str());
}

Answer from Aposhian on Stack Overflow

Microsoft Learn

learn.microsoft.com › en-us › dotnet › standard › base-types › standard-numeric-format-strings

Standard numeric format strings - .NET | Microsoft Learn

A standard numeric format string can be used to define the formatting of a numeric value in one of the following ways: It can be passed to the TryFormat method or an overload of the ToString method that has a format parameter.

ByteHide

bytehide.com › blog › c# tostring formatting: step-by-step tutorial

C# ToString Formatting: Step-By-Step Tutorial (2026)

December 31, 2023 - Formatting decimals into currency format is as simple as saying “Hello, World!” in C#. Have a look: ... Now, that’s a price tag with professionalism written all over it! Imagine an e-commerce platform where you’re showing product prices in various currencies. ToString("C") supports localization too!

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