MiniCRT/printf.c at master · SavedRest0Re/MiniCRT · GitHub

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#include "minicrt.h"

int fputc(int c, FILE* stream)
{
    if (fwrite(&c, 1, 1, stream) != 1)
        return EOF;
    else
        return c;
}
int fputs(const char* str, FILE* stream)
{
    int len = strlen(str);
    if (fwrite(str, 1, len, stream) != len)
        return EOF;
    else
        return len;
}

// ap = argument pointer
// lastarg 指向最后一个具名参数，即 format
// va_arg 获得下一个不定参数（假设已知其类型为 type）
// va_end 清理现场
#ifndef WIN32
#define va_list char*
#define va_start(ap, lastarg) (ap=(va_list)&lastarg+sizeof(lastarg))
#define va_arg(ap, type) (*(type*)((ap+=sizeof(type))-sizeof(type)))
#define va_end(ap) (ap=(va_list)0)
#else
#include <Windows.h>
#endif

int vfprintf(FILE* stream, const char* format, va_list arglist)
{
    int translating = 0;
    int ret = 0;
    const char* p = 0;
    for (p = format; *p != '\0'; ++p)
    {
        switch(*p)
        {
        case '%':
            if (!translating)
                translating = 1;
            else
            {
                if (fputc('%', stream) < 0)
                    return EOF;
                ++ret;
                translating = 0;
            }
            break;
        case 'd':
            if (translating)
            {
                char buf[16];
                translating = 0;
                itoa(va_arg(arglist, int), buf, 10);
                if (fputs(buf, stream) < 0)
                    return EOF;
                ret += strlen(buf);
            }
            else if (fputc('d', stream) < 0)
                return EOF;
            else
                ++ret;
            break;
        case 's':
            if (translating)
            {
                const char* str = va_arg(arglist, const char*);
                translating = 0;
                if (fputs(str, stream) < 0)
                    return EOF;
                ret += strlen(str);
            }
            else if (fputc('s', stream) < 0)
                return EOF;
            else
                ++ret;
            break;
        default:
            if (translating) // 根本不用判断
                translating = 0;
            if (fputc(*p, stream) < 0)
                return EOF;
            else
                ++ret;
            break;
        }
    }
    return ret;
}

int printf(const char* format, ...)
{
    va_list(arglist);
    va_start(arglist, format);
    return vfprintf(stdout, format, arglist);
}

int fprintf(FILE* stream, const char* format, ...)
{
    va_list(arglist);
    va_start(arglist, format);
    return vfprintf(stream, format, arglist);
}