Question

i have this function

char* copy(char* pString,...){
    char *vToate;
    int vLen;
    va_list vAp;
    va_start(vAp,pString);
    vLen+=strlen(pString);
    va_end(vAp);

    vToate=new char[vLen+1];

    va_list vAp1;
    va_start(vAp1,pString);
    strncpy(vToate,pString,strlen(pString));
    va_end(vAp1);
    return vToate;
}

if i try this

char *vTest="test";
char *vTmp=copy(vTest," ",vTest);
cout<<vTmp;

the result are “test” not “test test”
what are wrong ?

Answer 1

It looks you’re unclear about how to use variadic macros. You forgot to call va_arg to get each next element. You also need a length or sentinel value, so you can know when there aren’t any more arguments. It seems like you want this:

char *copy(char *str, ...)
{
    va_arg ap;
    va_start(str, ap);
    int len = 0;
    char *sp;
    for(sp=str; sp; sp=va_arg(ap, char*))
        len+=strlen(sp);
    va_end(ap);
    va_start(ap);
    char *dst = new char[len+1];
    int pos = 0;        
    for(sp=str; sp; sp=va_arg(ap, char*)){
        memcpy(dst+pos, sp, strlen(sp));
        pos+=strlen(sp);
    }
    va_end(ap);
    dst[pos] = '\0';
    return dst;
}

Which you would then call:

char *str = copy("foo", " ", "bar", NULL);