卡在myPrintf和va_arg列表中

Question

i'm currently working on my own implementation of scanf function, but i cannot use any library functions except for va_ macros.

Everything pretty much works except for printing stuff that is in *fmt variable and is not a %d, %s etc.

For example myPrintf("%d stuff and more stuff %s",50,"foo");

will print only 50foo and not 50 stuff and more stuff foo

I tried messing around with default part of swtich but it led me to nothing Thank you in advance!

void myPrintf(char *fmt, ...)
{
    va_list ap;
    char *s;
    char buf[64];
    va_start(ap, fmt);

    while(*fmt)
    {
        x++;
        switch(*fmt++)
        {
        case 's':
            s = va_arg(ap, char*);
            write(1,s,strlen(s));
            break;
        case 'd':
            s = toString(va_arg(ap, int));
            write(1,s,strlen(s));
            break;
        case 'b':
            s = toBin(va_arg(ap, int));
            write(1,s,strlen(s));
            break;
        default:
            break;
        }
    va_end(ap);
   }

}

Answer 1

It prints 50foo because it only prints when it saw "d" or "s" or "b" in fmt. You should check for "%" to print the arguments you give, and print characters from fmt otherwise. It should be something like the code below:

void myPrintf(char *fmt, ...)
{
    va_list ap;
    char *s;
    char c;
    char s2[100];
    char buf[64];
    va_start(ap, fmt);

    while(*fmt)
    {
        c = *fmt;
        if (c == '%') {
            fmt++;
            switch(*fmt)
            {
            case 's':
                s = va_arg(ap, char *);
                write(1, s, strlen(s));
                break;
            case 'd':
                memset(s2, 0, 100);
                sprintf(s2,"%d",va_arg(ap, int));
                write(1, s2, strlen(s2));
                break;
            default:
                break;
            }
        } else {
            write(1, fmt, 1);
        }
        va_end(ap);
        fmt++;
    }
    write(1, 0, 1);
}

Well, I edited your code a litte to make it work on my machine, since i don't have the implementations of toString() and toBin(). But, the implementation above will show you where you got it wrong. The code is checking for "%" symbol first, and when it saw "%" then it checks for "%s" and "%d" to print the arguments '50' and 'foo'. In all other cases, it prints characters from fmt, so 'stuff and more stuff' is also printed to stdin.