ビジュアルスタジオ2017を使用中にエラーが発生しました：fscanf_s

Question

char option; 
FILE *fp; 
errno_t err; 
err = fopen_s(&fp, "../AVL Trees/input.txt", "r"); 

while (!feof(fp)) 
{ 
    fscanf_s(fp, "%c", &option); //error is here 
    ... 
} 

これはAVL Treesプロジェクト用です。 私はなぜこのエラーが発生したのか理解できません： "十分な引数がフォーマットに渡されていません"、何か不足しましたか？

編集：

1>e:\visual studio projects\avl trees\avl trees\main.cpp(27): warning C4473: 'fscanf_s' : not enough arguments passed for format string 
1>e:\visual studio projects\avl trees\avl trees\main.cpp(27): note: placeholders and their parameters expect 2 variadic arguments, but 1 were provided 
1>e:\visual studio projects\avl trees\avl trees\main.cpp(27): note: the missing variadic argument 2 is required by format string '%c' 
1>e:\visual studio projects\avl trees\avl trees\main.cpp(27): note: this argument is used as a buffer size 

Answer 1

C標準（K.3.5.3.2 fscanf_s機能）から

4 The fscanf_s function is equivalent to fscanf except that the c, s, and [ conversion specifiers apply to a pair of arguments (unless assignment suppression is indicated by a *). The first of these arguments is the same as for fscanf. That argument is immediately followed in the argument list by the second argument, which has type rsize_t and gives the number of elements in the array pointed to by the first argument of the pair. If the first argument points to a scalar object, it is considered to be an array of one element.

でどこだから、この

fscanf_s(fp, "%c", &option, 1);