C语言 在提供函数指针时取消引用指向不完整类型的指针

Question

当我尝试运行以下代码时，我收到指向不完整类型错误的取消引用指针。我已经检查了有关此错误的其他几个问题，据我所知，这不是由于缺少或额外的结构关键字，我相信指针类型是正确的，但我可能弄错了。

代码可能还有其他问题，因为我只是在学习 C，我很高兴尝试自己解决它们，我似乎无法追踪不完整类型错误的问题。

Development/C/AI/test/src/test.c: In function ‘compare’:
Development/C/AI/test/src/test.c:10:19: error: dereferencing pointer to incomplete type ‘lrgraph_node {aka struct lrgraph_node}’
if ( strcmp(other->dataType, current->dataType == 0) ) {

测试.c

#include "lrGraph.h"
#include <string.h>
int data = 1;
char *dataType = "int";
lrgraph_edge *connected[] = {};
unsigned numEdges = 0;
int compare( lrgraph_node *other, lrgraph_node *current ) {
if ( strcmp(other->dataType, current->dataType == 0) ) {
return (int)other->data - (int)current->data;
}
return -1;
}
int main() {
lrgraph_node *nodeA = lrgraph_createNode((void*)&data, dataType, &compare, connected, numEdges);
lrgraph_printVersion();
}

lrGraph.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "lrGraph.h"
struct lrgraph_edge {
float weight;
lrgraph_node *nodeA;
lrgraph_node *nodeB;
};
struct lrgraph_node {
//data can be of any type
void *data;
//string to see if this node can be compared to another node based on data type
char *dataType;
int numEdges;
//comparator function which compares another node to this node
int (*compare)(lrgraph_node *other, lrgraph_node *current);
//array of connected edges
lrgraph_edge *connected[];
};
void lrgraph_printVersion() {
fprintf(stdout, "nlrgraph version 0.01bn");
}

lrgraph_node* lrgraph_createNode(void *data, char *dataType, int (*compare)(lrgraph_node* other, lrgraph_node* current), lrgraph_edge *connected[], unsigned numEdges) {
//allocate enough memory for the struct plus each pointer in the array of edges - https://stackoverflow.com/questions/32311269/can-we-have-a-struct-element-of-type-variable-length-array
lrgraph_node *node = malloc(sizeof(lrgraph_node) + numEdges * sizeof(lrgraph_edge));
if (NULL != node) {
node->data = data;
node->dataType = strdup(dataType);
node->compare = compare;
node->numEdges = numEdges;
//initialize each edge in the array
for( unsigned i=0; i < numEdges; i++) {
node->connected[i] = connected[i];
}
}
return node;
}

lrGraph.h

#ifndef LRGRAPH_H
#define LRGRAPH_H
typedef struct lrgraph_node lrgraph_node;
typedef struct lrgraph_edge lrgraph_edge;
lrgraph_node* lrgraph_createNode(void *data, char *dataType, int (*compare)(lrgraph_node *other, lrgraph_node *current), lrgraph_edge *connected[], unsigned numEdges);
void lrgraph_printVersion();
#endif /*LRGRAPH_H*/

Answer 1

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不完整类型"表示编译器看到您正在尝试使用结构类型，但没有该结构的定义。

如果您只使用指向结构的指针(实际上是在 C 中实现抽象数据类型的方式(，这很好，但如果您想取消引用此类指针，则结构定义必须是可见的。

在test.c中，只有lrGraph.h的内容是可见的(即typedef struct lrgraph_node lrgraph_node;(，但实际的struct lrgraph_node { ... };定义仅存在于lrGraph.c中。

可能的解决方案：将struct lrgraph_node { ... }定义移动到标头中。(或者，将compare的定义放入lrGraph.c(。