High level style of string manipulation in c language (IDFGH-10764)

[baldhead69]

Is your feature request related to a problem?

No response

Describe the solution you'd like.

I would like to suggest a better way to manipulate strings in c, ie, better and quickly way, mainly quickly way.
Something like a high level language like java for example, with several ready and easy to use methods to manipulate strings with static or dynamic memory allocation options.

This lib must be added in https://components.espressif.com/

Possible candidate:
I never used this lib, i find his suggestion on stackoverflow.

https://bstring.sourceforge.net/

Describe alternatives you've considered.

No response

Additional context.

No response

[0xjakob]

You can use the strings library of the C++ standard library in ESP-IDF.

What particular problems do you encounter or what particular features would you like to have?

[baldhead69]

But isn't the c++ library too heavy ?

And also not sure if i can mix c with c++, i think so, but....

[0xjakob]

But isn't the c++ library too heavy ?

Depends on what your requirements are. Hence me asking which problems you encounter. Have you tried using it on your project?

[baldhead69]

No. I never used c++ on esp32.

Just to really learn and code faster.

It's not the first time I've run into this "problem".
Actually I came across a simple "problem" of concatenating text, in my case constant text, with any variable, int or float or whatever. I know I can use snprintf, but buffer memory allocation is usually static and also requires several lines of code.
I think there is asprintf too, but....

Something like that only for int:

esp_err concat_text_int( const char* text, int number, const char** str )
{
    if( text == null || str == null )
    {
        ESP_LOGI();
        return err_arg;
    }

    size_t size = snprintf( NULL, 0, "%s%d", text, number ) + 1;  // +1 null character terminator.
    if( size < 0 )
        return ESP_FAIL;

    *str = (char*) malloc( size  );
    
    if( *str == null )
        return err_no_mem;

    size = snprintf( *str, size, "%s%d", text, number );
    if( size < 0 )
    {
        free( *str );
        return ESP_FAIL;
    }

    return ESP_OK;
}

[0xjakob]

In std::string, append, operator+= and insert all allow string concatenation. std::to_string converts numeric data to a string. Your function could be reduced to:

std::string concat_text_int(const char* text, int number)
{
    if (text == nullptr) 
    {
        throw std::invalid_argument("text was null");
    }

    std::string str(text);
    str.append(std::to_string(number));
    return str;
}

Note that you need to enable exceptions for this, but this all works and compiles on an ESP32.

The rest of the C++ standard library should cover most of the day-to-day programming needs for strings and also has more advanced concepts for rather special cases.

And also not sure if i can mix c with c++, i think so, but....

You can, it's perfectly legal. You need to consider language linking and designated initializers, though.

[baldhead69]

In std::string, append, operator+= and insert all allow string concatenation. std::to_string converts numeric data to a string. Your function could be reduced to:

std::string concat_text_int(const char* text, int number)
{
    if (text == nullptr) 
    {
        throw std::invalid_argument("text was null");
    }

    std::string str(text);
    str.append(std::to_string(number));
    return str;
}

Note that you need to enable exceptions for this, but this all works and compiles on an ESP32.

The rest of the C++ standard library should cover most of the day-to-day programming needs for strings and also has more advanced concepts for rather special cases.

And also not sure if i can mix c with c++, i think so, but....

You can, it's perfectly legal. You need to consider language linking and designated initializers, though.

I think str is local variable, no ?

I think i need to allocate this memory using new operator.

[0xjakob]

str is a local variable, that's correct. But it will automatically be transferred to the caller on return, if that is your concern.

You don't need to manually allocate or de-allocate memory when using std::string. The library does that automatically (like in Java or other high-level languages).

[baldhead69]

str is a local variable, that's correct. But it will automatically be transferred to the caller on return, if that is your concern.

You don't need to manually allocate or de-allocate memory when using std::string. The library does that automatically (like in Java or other high-level languages).

C++ doen't have garbage collector, right ?

And local variables no longer exist outside the function.

If std::string allocate memory implicitly, i need to deallocate later, i just don't know if it use free or delete for this.

[0xjakob]

C++ doen't have garbage collector, right ?

No, it does not. But it has automatic destruction, which ensures that all memory is deallocated without user interaction (if the type supports it, and std::string does). This is called RAII.

And local variables no longer exist outside the function.

Yes, but if they are returned, they are automatically transferred to calling function. Transfer can mean copying the object, moving it, or, if the compiler is able to optimize, constructing the local variable directly in the scope of the calling function. This all happens automatically for std::string and all its allocated memory, you do not need to decallocate it yourself.

Even if you are not programming in C++, it might be a good chance to consider switching to it, if just for the parts dealing with strings. The C++ standard library has several advantages for users as well as for us:

• Many parts, like std::string, are build with automatic resource management which prevents errors, e.g. accidental memory leaks. This is impossible in C. Automatic resource management is also something that gives you a lot of convenience when dealing with strings (you asked for easy to use methods and quicker coding)
• It is actively maintained and heavily tested
• It comes with the upstream tool chain, which means we don't need to maintain it ourselves, giving us more time to fix bugs and improve other aspects of ESP-IDF.
• It has more advanced concepts, e.g. std::string_view, which allows light-weight string wrappers around pre-defined memory (you asked for static memory allocation options as well)

If you cannot use C++ for whatever reason, nothing should stop you from integrating any C library you want. If something is indeed stopping you from doing that, please let us know. The component registry has also been opened recently, so anyone can add their components there.

[baldhead69]

@0xjakob,

Very good explanation.

The below doubt is valid both for c and c++ :

If i pass a string dynamic allocated (by pointer) to another lib, like network lib for example, to send this message by wifi.

How to know the right time to release the resource ( here the dynamically allocated memory for the string ) ?

• if the string is copied, there is no problem.
• if the string is passed by pointer, the string could only be deallocated when the network lib had sent the message ( with this string ).

Thank's.

[0xjakob]

How to know the right time to release the resource?

If you pass a char pointer, it depends on the library you are using when you can release the underlying memory. But this is not something a string library can help you with.

[baldhead69]

How to know the right time to release the resource?

If you pass a char pointer, it depends on the library you are using when you can release the underlying memory. But this is not something a string library can help you with.

Yes, i know.

In the case of websocket server, would you know how to inform me ?
Or does it depend on some setting ?

Complicated to know when release resource when dealing with network library.

Thank's.

[0xjakob]

In the case of websocket server, would you know how to inform me ?
Or does it depend on some setting ?

Still assuming that you pass char pointers, it again depends on the library. But if you stick to C, you have to manage your memory yourself. I'm afraid this is not something ESP-IDF can help you with, and it is not the purpose of ESP-IDF to manage a user's memory, either.

[0xjakob]

@baldhead69 If there are no other questions, could we close this issue?

[baldhead69]

@0xjakob ,

Yes, i can close.

Could you help me open this below issue again, i don't know why it was closed

#11903