Question

I made a function in C, that concatenates a variable number of strings.
That’s my code:

char* texto(const char* s, ...){
        va_list args;
        char *tmp;
        char *res;
        size_t len = strlen(s);

        // pega um handle ao início da lista de parâmetros
        va_start(args, s);
        // calcula o tamanho total de todas as strings - pega o próximo parâmetro da lista, até chegar no NULL
        while ((tmp = va_arg(args, char*))){
            len += strlen(tmp);
        }
        va_end(args);

        res = malloc(len+1);
        if (!res){
                fprintf(stderr, "Erro ao alocar string. Função 'texto'\n");
                exit(EXIT_FAILURE);
        }

        // cria a string concatenada
        strcpy(res, s);

        va_start(args, s);
        // pega o próximo parâmetro da lista, até chegar no NULL
        while ((tmp  = va_arg(args, char*))){ 
            strcat(res, tmp); 
        }
        va_end(args);

        return res;
}

I’m using like this:

char* txt = texto("a", "b", "c", "d", "e", NULL);
//txt is now: "abcde"

It works fine.
But I can’t pass numeric parameters to this function, only strings.
I need to change the function to work like this:

char* txt = texto("a", "b", 1, "d", 4.5, "e", NULL);
//txt is now: "ab1d4.5e"

How can I do that?
How I get parameters with diferent types using va_arg()?

The solution I found until now is create a function int2str():

inline char* int2str(int inteiro){
    char* str = malloc(10);
    sprintf(str, "%d", inteiro);
    return str;
}

But I have to use this way:

char* txtnum = int2str(23);
char* txt = texto("a", txtnum, NULL);
free(txtnum);

otherwise, I got a memory leak…

I could use the function int2str() inside the function texto() but I don’t know how to check the type of the parameters!

Ps.: I’m using C, not C++ for my code.

Answer 1

If you’re willing to take a gcc specific solution you can change int2str to be this macro:

# define int2str(i)                                                           \
  (__extension__                                                              \
    ({                                                                        \
      char *new = (char *) __builtin_alloca (10);                        \
      sprintf(new, "%d", i); \
      new;                                  \
    }))

This then means you can write:

char* txt = texto("a", int2str(23), NULL);

without leaking. It’s very non portable though.