平衡字符与文件结束符的问题

   昨天写了一个小程序，关于平衡符号的。运行正常，只是每次输出都重复一遍，例如：
   从input.txt文件读入数据{[()]}，其实input.txt中只有一行数据
   

{[()]}

，输出本应该是

{[()]} : RIGHT!

但是，真正输出是：

{[()]} : RIGHT!
{[()]} : RIGHT!

几经查找，原来是fscanf和feof的原因.对于一个0字节文件，只有read一次，feof才会认为到达了文件结尾（原以为，对于0字节文件，feof会直接判断出到达了文件结尾）。我先前的程序如下

.......................
while(feof(fp)){
    fscanf(....);
}

.......................

这样造成，即使文件已经到达了文件结尾，但是feof不会返回true，反而继续执行循环，当fscanf被执行后，此时feof才会认为到达了文件结尾(造成多执行一次循环)。所以判断文件结尾应该放在fscanf之后：

....................... while(1){     fscanf(....);     if(feof(fp))         break; }

.......................

附上平衡字符的源码：

#include
#include
#include
#include "Stack.h"

#define F_INPUT "input.txt"
#define M_INPUT "r"
#define MAXBUFSIZE 80

int main()
{
        FILE *fp;
        Stack *s;
        char buf[MAXBUFSIZE], c, k;
        int i, flag;
        if((fp = fopen(F_INPUT, M_INPUT)) == NULL){
                printf("Can not open input file\n");
                return 1;
        }
        if( (s = (Stack *)malloc(sizeof(Stack))) == NULL){
                printf("Fail to stack allocation\n");
                return 1;
        }
        initStack(s);
        while(1){
                flag = 0;
                fscanf(fp, "%s", buf);
                if(feof(fp) || ferror(fp))
                        break;
                //printf("%s\n", buf);
                for(i = 0;i < strlen(buf);i++){
                        c = buf[i];
                        if(c == '{' || c == '[' || c == '(')
                                pushStack(s, c);
                        else if(c == '}' || c == ']' || c == ')'){
                                if(emptyStack(s)){
                                       flag = 1;
                                        break;
                                }
                                popStack(s, &k);
                                //printf("k = %c\n", k);
                                if((c == '}' && k == '{') || (c == ']' && k == '[') || (c == ')' || k == '('))
                                        continue;
                                else{
                                        flag = 1;
                                        break;
                                }
                        }
                }
                if(!emptyStack(s))
                        flag = 1;
                if(flag)
                        printf("%s : ERROR!\n", buf);
                else
                        printf("%s : RIGHT!\n", buf);
        }
        fclose(fp);
        return 0;
}