[英]Struct and char**
我最近在C编程中是全新的,我开始更多地研究指针,我遇到了代码问题。
所以我尝试将一个字符串传递给一个结构中的char**
,但我总是遇到错误。 在此先感谢这里是一些代码
这是我使用的结构。
typedef struct Queue {
int capacity;
int front;
int rear;
int size;
char **car_id;
};
这就是我试图加入的内容。 如果你能看到我尝试strcpy
但失败了。 即使我把&或*。
printf("Printing the contect of the TXT file\n");
int countS=-1,countQ=-1;
char line[10];
FILE *fp;
fp = fopen("car.txt","r");
if (fp == NULL) {
printf("Error: File doesn't exist exiting the programm!");
exit(1);
}
while(!feof(fp)){
fgets(line,10,fp);
printf("%s",line);
if(line[(strlen(line))-2]=='Q'){
countQ++;
line[strlen(line)-2] = 0;
strcpy(car_id,line);
strcpy(QBoat->car_id[countQ],car_id);
QBoat->rear=countQ;
QBoat->front=0;
QBoat->size=countQ;
}else if(line[(strlen(line))-2]=='S'){
countS++;
line[strlen(line)-2] = 0;
SBoat->top = countS;
//strcpy(SBoat->car_id[countS],line);
}
}
fclose(fp);
使用结构很容易搞乱内存分配和释放。 因此,最好始终为每个结构编写new和destroy函数。
/* To avoid confusion, it's best to declare structs as type definitions
and name them Something_t. Capital letter to avoid conflict with
built in types, _t to note that it is a type, and to avoid conflict
with other names. */
typedef struct {
/* Using size_t means less type casting */
size_t capacity;
int front;
int rear;
int size;
char **items;
} Queue_t;
Queue_t *Queue_new( const size_t capacity ) {
/* Use calloc because we have to zero everything anyway */
Queue_t *queue = calloc( 1, sizeof(Queue_t) );
/* Allocate enough space to store a list of whatever
queue->items is a list of */
queue->capacity = capacity;
queue->items = malloc( capacity * sizeof(*(queue->items)) );
return queue;
}
void Queue_destroy( Queue_t *queue ) {
/* Since items were copied into the list, it's the queue's responsibility
to free them */
for( int i = queue->front; i < queue->rear; i++ ) {
free( queue->items[i] );
}
/* Now free the list of items */
free( queue->items );
/* And finally the struct itself */
free( queue );
}
现在已经分配了结构及其项目列表,您必须确保不添加太多项目。 添加到队列的代码永远不会检查它是否超出了队列的容量。 因此,最好编写一个函数来添加能够正确检查容量的项目。
void Queue_add( Queue_t *queue, const char *item ) {
if( queue->size >= (int)queue->capacity ) {
fprintf(stderr, "Queue capacity of %zu exceeded!\n", queue->capacity);
exit(1);
}
/* You used strcpy in your example, so I'm following that.
You could also not copy and store the original pointer. */
queue->items[ queue->rear ] = strdup( item );
/* I don't know if this is right */
queue->rear++;
queue->size++;
}
排队逻辑可能是错误的,我对队列不好,但你明白了。 您甚至可以稍后扩展队列以自动调整自身大小。
现在,您可以单独测试这些工作。 一旦确定它们有效,您可以尝试从文件中读取并使用队列功能。
int main() {
char filename[] = "car.txt";
FILE *fp = fopen(filename,"r");
if (fp == NULL) {
fprintf(stderr, "Couldn't read '%s': %s\n", filename, strerror(errno));
exit(1);
}
/* Just picked a number out of thin air */
Queue_t *qboats = Queue_new(256);
Queue_t *sboats = Queue_new(256);
char line[10];
while( fgets( line, 10, fp) != NULL ) {
size_t len = strlen(line);
/* Choose the right queue to use */
Queue_t *queue;
switch ( line[len-2] ) {
case 'S':
queue = sboats;
break;
case 'Q':
queue = qboats;
break;
default:
fprintf( stderr, "Can't understand line '%s'\n", line );
continue;
break;
}
/* Chop off the identifier */
line[len - 2] = '\0';
/* Add to the queue */
Queue_add( queue, line );
}
/* Do something with the queues. This should probably be Queue_print(). */
for( int i = qboats->front; i < qboats->rear; i++ ) {
printf("qboat: %s\n", qboats->items[i]);
}
for( int i = sboats->front; i < sboats->rear; i++ ) {
printf("sboat: %s\n", sboats->items[i]);
}
/* Now clean them up */
Queue_destroy( sboats );
Queue_destroy( qboats );
}
现在大部分工作都在确定要使用的队列。
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