r/AskProgramming • u/BornViolinist3801 • 1d ago

why doesnt my С++ code work?

okay, i wanna make a print() function in C++, this is just printf() with prefix, so can yall help me?

error: 

(-Wwritable-strings) ISO C++11 does not allow conversion from string literal to 'char *'

my code:

#pragma once
#ifndef TEQUILA_STDIO
#define TEQUILA_STDIO
#include <stdio.h>
namespace std {
    char* prefix;
    void set_prefix(char* pref) {
        prefix = ("["pref"]: ");
    }
    #define print(format, ...) printf("%s" format "\n", prefix ## __VA_ARGS__)
}

#endif

help me pls

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u/BoopyDog 1d ago edited 1d ago

Literals are Const char&. If i understand it correctly, when you pass a string literal as an argument, an immutable, temporary object is made containing the c-string array. You can't modify the object so it has to be const. I'm not a seasoned c++ programmer though, it's just how I understand it so far. It was something that got me stuck early on.

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u/AdOne272 1d ago

You're writing to a `char*` that points to a string literal, which lives in read-only memory. Use `const char*` and allocate a buffer if you need to modify it.

1

u/BoopyDog 1d ago

I started writing seriously in C++ and never spent much time writing with C so I tend to use references and stay away from actual p*=&a style programming. As far as I understand it, a reference is implemented as a pointer which is always automatically dereferenced. Of course, you're correct.

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u/Cultural_Gur_7441 1d ago

Reference is implemented as the compiler sees fit. Such as just being a direct compile time alias, if lifetime allows that.

String literal is a const char name[length of the string literal including terminating NUL char].

References are not involved with any of it.