在我的系统上,以下输出213两次但是有保证吗？
标准中的语言(C99或C11)似乎没有明确指出原始值应保持不变(无论是否不确定).
#include <stdio.h> int main() { int d = 213; // matching failure sscanf("foo","%d",&d); printf("%d\n",d); // input failure sscanf("",d); }
解决方法
7 A directive that is a conversion specification defines a set of matching input sequences,as described below for each specifier. A conversion specification is executed in the following steps:
8 […]
9 An input item is read from the stream,unless the specification includes an n specifier. An input item is defined as the longest sequence of input characters which does not exceed any specified field width and which is,or is a prefix of,a matching input sequence.285) The first character,if any,after the input item remains unread. If the length of the input item is zero,the execution of the directive fails; this condition is a matching failure unless end-of-file,an encoding error,or a read error prevented input from the stream,in which case it is an input failure.
10 Except in the case of a % specifier,the input item (or,in the case of a %n directive,the count of input characters) is converted to a type appropriate to the conversion specifier. If the input item is not a matching sequence,the execution of the directive fails: this condition is a matching failure. Unless assignment suppression was indicated by a *,the result of the conversion is placed in the object pointed to by the first argument following the format argument that has not already received a conversion result. […]
对我来说,单词“step”和“如果输入项的长度为零,指令的执行失败”表示如果输入与格式中的说明符不匹配,则解释在该说明符的任何赋值之前停止发生了.
另一方面,关于引用的子条款4清楚地说明了指定失败者的说明符,再次使用适合于有序事件序列的语言：
4 The fscanf function executes each directive of the format in turn. When all directives have been executed,or if a directive fails (as detailed below),the function returns.
