pirntf()的返回

pirntf();的返回值是一个int值，表示被打印的字符数

如 int retno=printf("%d",90); //retno=2 

int retno=printf("123n"); //retno=4 包含换行字符
printf("%d",printf("%d",printf("%d",43)));的输出是4321

输出由里到外如果是失败，返回值为负数，并设置错误指示符

Return Value

On success, the total number of characters written is returned.

If a writing error occurs, the error indicator (ferror) is set and a negative number is returned.

If a multibyte character encoding error occurs while writing wide characters, errno is set to EILSEQ and a negative number is returned.