C++ fscanf / fscanf_s 行为差异
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fscanf / fscanf_s difference in behaviour
提问by Ofek Shilon
I'm puzzled by the following difference in behaviour:
我对以下行为差异感到困惑：
// suppose myfile.txt contains a single line with the single character 's'
errno_t res;
FILE* fp;
char cmd[81];
res = fopen_s(&fp, "D:\myfile.txt", "rb" );
fscanf(fp,"%80s",cmd); // cmd now contains 's/0'
fclose(fp);
res = fopen_s(&fp, "D:\myfile.txt", "rb" );
fscanf_s(fp,"%80s",cmd); // cmd now contains '/0' !
fclose(fp);
The results do not depend in the order of call (i.e., call fscanf_s first, you'd get the empty string first). Compiled on VC++ - VS2005. Can anyone reproduce? Can anyone explain?
结果不依赖于调用顺序（即首先调用 fscanf_s，您将首先获得空字符串）。在 VC++ - VS2005 上编译。任何人都可以复制吗？谁能解释一下？
Thanks!
谢谢！
回答by Michael Burr
From the docs on fscanf_s(), http://msdn.microsoft.com/en-us/library/6ybhk9kc.aspx:
从文档上fscanf_s()，http: //msdn.microsoft.com/en-us/library/6ybhk9kc.aspx：
The main difference between the secure functions (with the _s suffix) and the older functions is that the secure functions require the size of each c, C, s, S and [ type field to be passed as an argument immediately following the variable. For more information, see scanf_s, _scanf_s_l, wscanf_s, _wscanf_s_l and scanf Width Specification.
安全函数（带有 _s 后缀）与旧函数之间的主要区别在于，安全函数要求将每个 c、C、s、S 和 [ 类型字段的大小作为紧跟在变量之后的参数传递。有关详细信息，请参阅 scanf_s、_scanf_s_l、wscanf_s、_wscanf_s_l 和 scanf 宽度规范。
And http://msdn.microsoft.com/en-us/library/w40768et.aspx:
和http://msdn.microsoft.com/en-us/library/w40768et.aspx：
Unlike scanf and wscanf, scanf_s and wscanf_s require the buffer size to be specified for all input parameters of type c, C, s, S, or [. The buffer size is passed as an additional parameter immediately following the pointer to the buffer or variable. For example, if reading a string, the buffer size for that string is passed as follows:
char s[10];
scanf("%9s", s, 10);
与 scanf 和 wscanf 不同，scanf_s 和 wscanf_s 要求为 c、C、s、S 或 [ 类型的所有输入参数指定缓冲区大小。缓冲区大小作为附加参数传递，紧跟在指向缓冲区或变量的指针之后。例如，如果读取一个字符串，则该字符串的缓冲区大小按如下方式传递：
字符 [10];
scanf("%9s", s, 10);
So you should call it like so:
所以你应该这样称呼它：
fscanf_s(fp,"%80s",cmd, sizeof(cmd));
回答by Michael Mrozek
fscanf_s(and the whole scanf_sfamily) requires that you pass the size of any %c, %C, %s, %S, or %[after the buffer itself; you're omitting that argument:
fscanf_s（以及整个scanf_s系列）要求您传递任何%c, %C, %s, %S, 或%[缓冲区本身之后的大小；你忽略了这个论点：
fscanf_s(fp, "%80s", cmd, 81);
回答by Puppy
Your question is tagged C++ and you're compiling in VC++, but using fscanf? Get a std::ifstream.
您的问题被标记为 C++ 并且您正在 VC++ 中进行编译，但是使用 fscanf？获取 std::ifstream。
std::string buffer;
std::ifstream fp("my filepath");
fp >> buffer;
