C：多个文件的结构列表和fscanf

Question

作为一个项目，我必须读取多个表格分隔文件(包含从左上角的 0,0 开始的 x 和 y 坐标(并将内容保存在动态分配的链表中。通过一次读取，一切都很好，但是当我阅读并尝试将第二个文件的元素附加到列表中时，这些项目不会以某种方式附加。

有人可以帮助我找到错误的位置以及如何解决它吗？我是否对列表中的指针做错了？

结构：

typedef enum{
BLUME=-1, FREI
}belegung;
typedef struct position{
int zeile;
int spalte;
belegung element;
struct position* next;
}position;
typedef struct feld{
int zeilen;
int spalten;
int anzBlumen;
position* positionen;
}feld;

读取和添加元素的函数：

int read(feld* f, char* file){
FILE* in;
if((in = fopen(file, "r")) == NULL)
return -1;

int count = 0;
if (f->zeilen == 0 && f->spalten == 0 && f->positionen == NULL)
count = firstread(in, f);
else {
printf("already have flowersn");
int a, b;
int oldS = f->spalten;
position* ptr = f->positionen; // CAUTION: p = NULL
while (ptr != NULL) {
ptr = ptr->next;
if (ptr != NULL)
printf("readA: ptr @ %p -> (%d, %d) = %dn", ptr, ptr->zeile,
ptr->spalte, ptr->element);
}
// read first line
if (fscanf(in, "%dt%d", &a, &b) != EOF) {
f->zeilen = max(f->zeilen, a);
f->spalten = oldS + b;
count++;
}
// read first flower

if (fscanf(in, "%dt%d", &a, &b) != EOF) {
ptr = calloc(1, sizeof(position));
ptr->zeile = a;
ptr->spalte = b + oldS;
ptr->element = -1;
ptr->next = NULL;
count++;
printf("Flower: (%d, %d)->(%d, %d) at %pn", a, b, ptr->zeile,
ptr->spalte, ptr);
}
// read flower lines
while (fscanf(in, "%dt%d", &a, &b) != EOF) {
ptr->next = calloc(1, sizeof(position));
ptr = ptr->next;
ptr->zeile = a;
ptr->spalte = b + oldS;
ptr->element = -1;
ptr->next = NULL;
printf("Flower: (%d, %d)->(%d, %d) at %pn", a, b, ptr->zeile,
ptr->spalte, ptr);
count++;
}
f->anzBlumen += count - 1;
}

printf("Flowerscan donen");
// get 'next' to write element in ptr
preinitFreefeld(f);
//setFreefeld(f);
printf("setting up free field donen");
fclose(in);
return count;
}
int firstread(FILE* in, feld* f) {
int a, b;
position* p = NULL;
int count = 0;
// read first line
if (fscanf(in, "%dt%d", &a, &b) != EOF) {
f->zeilen = a;
f->spalten = b;
count++;
}
// read first flower
p = calloc(1, sizeof(position));
position* ptr = p;
if (fscanf(in, "%dt%d", &a, &b) != EOF) {
ptr->zeile = a;
ptr->spalte = b;
ptr->element = BLUME;
ptr->next = NULL;
count++;
}
f->positionen = p;
// read flower lines
while (fscanf(in, "%dt%d", &a, &b) != EOF) {
if (ptr->next == NULL)
ptr->next = calloc(1, sizeof(position));
ptr = ptr->next;
ptr->zeile = a;
ptr->spalte = b;
ptr->element = BLUME;
ptr->next = NULL;
count++;
}
f->positionen = p;
f->anzBlumen = count - 1;
return count;
}

示例输入文件：

3   5
2   2
2   3
0   0
0   1
2   4
1   4
0   2

在该输入中，第一行指定要在屏幕上使用的行数和行数，下一行放置元素，行中的第一个数字是行或 x in (x， y(。

示例输出：

-1  -1  -1  0   0
0   0   0   0   -1
0   0   -1  -1  -1

Answer 1

当我阅读并尝试将第二个文件的元素附加到列表中时，这些项目不会以某种方式附加。

看看这个代码：

position* ptr = f->positionen; // CAUTION: p = NULL
while (ptr != NULL) {
ptr = ptr->next;
if (ptr != NULL)
printf("readA: ptr @ %p -> (%d, %d) = %dn", ptr, ptr->zeile,
ptr->spalte, ptr->element);
}

在这里，您继续ptr直到为 NULL。换句话说，ptr不再指向列表中的元素。您可能想要：

while (ptr->next != NULL) {

然后你想附加新元素使用

ptr->next = calloc(1, sizeof(position)

但是你有：

if (fscanf(in, "%dt%d", &a, &b) != EOF) {
ptr = calloc(1, sizeof(position));
^^^^

这意味着新元素不会从readfirst附加到列表中，而是启动一个新的链表。

我还没有研究过您的代码的所有细节，但我认为您将代码更改为以下内容：

if (f->positionen == NULL)    // Only check for pointer being NULL
count = firstread(in, f);
else {
printf("already have flowersn");
int a, b;
int oldS = f->spalten;
position* ptr = f->positionen;
while (ptr->next != NULL) {    // Check for ptr->next
ptr = ptr->next;
// if (ptr != NULL)  Delete this line - not needed anymore
printf("readA: ptr @ %p -> (%d, %d) = %dn", ptr, ptr->zeile,
ptr->spalte, ptr->element);
}
// read first line
if (fscanf(in, "%dt%d", &a, &b) != EOF) {
f->zeilen = max(f->zeilen, a);
f->spalten = oldS + b;
count++;
}
// Delete this block - you already have a "first flower"
// read first flower
//if (fscanf(in, "%dt%d", &a, &b) != EOF) {
//    ptr = calloc(1, sizeof(position));
//    ptr->zeile = a;
//    ptr->spalte = b + oldS;
//    ptr->element = -1;
//    ptr->next = NULL;
//    count++;
//    printf("Flower: (%d, %d)->(%d, %d) at %pn", a, b, ptr->zeile,
//            ptr->spalte, ptr);
//}
// read flower lines
while (fscanf(in, "%dt%d", &a, &b) != EOF) {
ptr->next = calloc(1, sizeof(position));
ptr = ptr->next;
ptr->zeile = a;
ptr->spalte = b + oldS;
ptr->element = -1;
ptr->next = NULL;
printf("Flower: (%d, %d)->(%d, %d) at %pn", a, b, ptr->zeile,
ptr->spalte, ptr);
count++;
}
f->anzBlumen += count - 1;
}