C 如何循环遍历文件的每一行？

我试图为文件中的每一行分配一个新结构的内存，但当文件为空时，我的循环仍会分配一次内存。问题在于使用while（！feof（file）），但我无法找到while循环的替代检查方法

循环如下所示：

while(!feof(f))
{
    p = (struct PlayerTime*)malloc(sizeof(struct PlayerTime));
    head = p;
    fscanf(f, "%f %s", &p->seconds, p->name);
    p = p->next;
}

// Allocate the space for the first element
struct PlayerTime *head=malloc(sizeof(*head));
// p will always point to a pointer to the element to be filled;
// let's start with the head
struct PlayerTime **p=&head;
// Try to read
while(fscanf(f, "%f %s", &((*p)->seconds), (*p)->name)==2)
{
    // If we are here, the last read was successful
    // Move p to the pointer to the next element
    p = &((*p)->next);
    // ... and allocate the space for such element
    *p = malloc(sizeof(**p));
}
// After exit, there's an extra element that we allocated but we couldn't read
// Free it
free(*p);
// And put the relevant pointer to NULL
// (it will terminate the list, or set head to NULL if no element has been read)
*p=NULL;

指针和结构都是在循环之前定义的，如果文件中没有任何内容，我就不知道如何让它不循环

feof（f）

表示

EOF

尚未命中

fscanf

点击

EOF

并失败

feof（f）

停止循环，因为已命中

EOF

正确的方法：

while (fscanf(f, "%f %s", &p->seconds, p->name) == 2) {
    ...
}

提示：还要花更多的时间思考何时以及如何分配内存，可能会发生什么情况，以及应该如何处理这些情况。

这一点已经讨论得非常透彻

feof

不会告诉您文件是否将在下一次读取时完成，但会告诉您是否已尝试读取但由于文件结束而失败

在您的情况下，解决方案是检查读取是否失败（通过检查

fscanf

的返回值），在这种情况下，取消分配结构；这也使您的代码更加健壮，因为它还检查EOF以外的错误（例如IO错误、无效数据格式等）

顺便说一句，

p=p->next

不会实现您的期望。如果您正在“动态”构建链接列表，您可以执行以下操作：

while(!feof(f))
{
    p = (struct PlayerTime*)malloc(sizeof(struct PlayerTime));
    head = p;
    fscanf(f, "%f %s", &p->seconds, p->name);
    p = p->next;
}

// Allocate the space for the first element
struct PlayerTime *head=malloc(sizeof(*head));
// p will always point to a pointer to the element to be filled;
// let's start with the head
struct PlayerTime **p=&head;
// Try to read
while(fscanf(f, "%f %s", &((*p)->seconds), (*p)->name)==2)
{
    // If we are here, the last read was successful
    // Move p to the pointer to the next element
    p = &((*p)->next);
    // ... and allocate the space for such element
    *p = malloc(sizeof(**p));
}
// After exit, there's an extra element that we allocated but we couldn't read
// Free it
free(*p);
// And put the relevant pointer to NULL
// (it will terminate the list, or set head to NULL if no element has been read)
*p=NULL;

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除了上面的链接，请参见对已接受答案的评论。