对于这个问题,我见过的最优雅的解决方案是 Sean Barrett 的writefv
,用于他的微型图像编写库stb_image_write
,可在此处获得。他只实现了一些原语(并且没有错误处理),但同样的方法可以扩展到基本上是二进制文件printf
(对于阅读,你可以做同样的事情来获得一个二进制文件scanf
)。非常优雅整洁!其实整个事情就是这么简单,我不妨把它包括在这里:
static void writefv(FILE *f, const char *fmt, va_list v)
{
while (*fmt) {
switch (*fmt++) {
case ' ': break;
case '1': { unsigned char x = (unsigned char) va_arg(v, int); fputc(x,f); break; }
case '2': { int x = va_arg(v,int); unsigned char b[2];
b[0] = (unsigned char) x; b[1] = (unsigned char) (x>>8);
fwrite(b,2,1,f); break; }
case '4': { stbiw_uint32 x = va_arg(v,int); unsigned char b[4];
b[0]=(unsigned char)x; b[1]=(unsigned char)(x>>8);
b[2]=(unsigned char)(x>>16); b[3]=(unsigned char)(x>>24);
fwrite(b,4,1,f); break; }
default:
assert(0);
return;
}
}
}
以下是他使用它编写真彩色 .BMP 文件的方式:
static int outfile(char const *filename, int rgb_dir, int vdir, int x, int y, int comp, void *data, int alpha, int pad, const char *fmt, ...)
{
FILE *f;
if (y < 0 || x < 0) return 0;
f = fopen(filename, "wb");
if (f) {
va_list v;
va_start(v, fmt);
writefv(f, fmt, v);
va_end(v);
write_pixels(f,rgb_dir,vdir,x,y,comp,data,alpha,pad);
fclose(f);
}
return f != NULL;
}
int stbi_write_bmp(char const *filename, int x, int y, int comp, const void *data)
{
int pad = (-x*3) & 3;
return outfile(filename,-1,-1,x,y,comp,(void *) data,0,pad,
"11 4 22 4" "4 44 22 444444",
'B', 'M', 14+40+(x*3+pad)*y, 0,0, 14+40, // file header
40, x,y, 1,24, 0,0,0,0,0,0); // bitmap header
}
(write_pixels
省略的定义,因为它在这里很切线)