'(' 标记之前的预期构造函数、析构函数或类型转换

Question

我是编程新手。我刚刚学习了 c++ 和一些数据结构的概念。 我正在尝试使用邻接表编写图形表示。 我使用代码块作为我的编译器。但是，每当我尝试编译我的程序时，我都会收到以下错误...

C:\Users\Garg\Desktop\try\Stack.cpp|22|错误：变量或字段“initialize_graph”声明为无效| C:\Users\Garg\Desktop\try\Stack.cpp|22|error: ',' 标记之前的预期主表达式| C:\Users\Garg\Desktop\try\Stack.cpp|22|错误：“int”之前的预期主表达式| C:\Users\Garg\Desktop\try\Stack.cpp|23|错误：变量或字段“read_graph”声明为无效| C:\Users\Garg\Desktop\try\Stack.cpp|23|error: ',' token| 之前的预期主表达式| C:\Users\Garg\Desktop\try\Stack.cpp|23|错误：“int”之前的预期主表达式| C:\Users\Garg\Desktop\try\Stack.cpp|24|错误：变量或字段 'insert_edge' 声明为 void| C:\Users\Garg\Desktop\try\Stack.cpp|24|错误：',' 标记之前的预期主表达式| C:\Users\Garg\Desktop\try\Stack.cpp|24|错误：'int'之前的预期主表达式| C:\Users\Garg\Desktop\try\Stack.cpp|24|错误：'int'之前的预期主表达式| C:\Users\Garg\Desktop\try\Stack.cpp|24|错误：'int'之前的预期主表达式| C:\Users\Garg\Desktop\try\Stack.cpp|25|错误：变量或字段 'print_graph' 声明为 void| C:\Users\Garg\Desktop\try\Stack.cpp|25|错误：')' 标记之前的预期主表达式| C:\Users\Garg\Desktop\try\Stack.cpp||在函数'int main()':| C:\Users\Garg\Desktop\try\Stack.cpp|32|错误：'read_graph' 未在此范围内声明| C:\Users\Garg\Desktop\try\Stack.cpp|33|错误：'print_graph' 未在此范围内声明| C:\Users\Garg\Desktop\try\Stack.cpp|36|错误：变量或字段 'initialize_graph' 声明为 void| C:\Users\Garg\Desktop\try\Stack.cpp|36|错误：'g' 未在此范围内声明| C:\Users\Garg\Desktop\try\Stack.cpp|36|错误：'int'之前的预期主表达式| C:\Users\Garg\Desktop\try\Stack.cpp|46|错误：变量或字段“read_graph”声明为无效| C:\Users\Garg\Desktop\try\Stack.cpp|46|错误：'g' 未在此范围内声明| C:\Users\Garg\Desktop\try\Stack.cpp|46|错误：'int'之前的预期主表达式| ||=== 构建完成：21 个错误，0 个警告 ===|

这是我的程序：

#include<iostream>
#define MAXV 1000       /* maximum number of vertices */
using namespace std;
struct node
{ 
int y;              /*adjacency info*/
int weight;             /* edge weight, if any */
struct node *next;      /* next edge in list */
} edgenode;

struct graph{
node *edges[MAXV+1];     /* adjacency info */
int degree[MAXV+1];             /* outdegree of each vertex */
int nvertices;          /* number of vertices in graph */
int nedges;             /* number of edges in graph */
int directed;           /* is the graph directed? */
} graph;
void initialize_graph (graph *, int);
void read_graph (graph *, int);
void insert_edge (graph *, int, int, int);
void print_graph (graph *);

int main()
{
struct graph *g = NULL;
cout << "Now reading graph";
read_graph(g, 1);
print_graph(g);
return 0;
}
void initialize_graph(graph *g, int directed)
{
int i;
g -> nvertices = 0;
g -> nedges = 0;
g -> directed = directed;
for (i=1; i<=MAXV; i++) g->degree[i] = 0;
for (i=1; i<=MAXV; i++) g->edges[i] = NULL;
}

void read_graph(graph *g, int directed)
{
int i;
int m;
int x, y;           /* vertices in edge (x,y) */
initialize_graph(g, directed);
cout << "Enter the number of vertivces and edges";
cin >> g->nvertices;
cin >> m;
cout << "Enter the vertices for the edge and the weight of the edge";
for (i=1; i<=m; i++) {
cin >> x;
cin >> y;
insert_edge(g,x,y,directed);
}
}

void insert_edge(graph *g, int x, int y, int directed)
{
struct node *p;
p = malloc(sizeof(struct node));
p->weight = NULL;
p->y = y;
p->next = g->edges[x];
g->edges[x] = p; /* insert at head of list */
g->degree[x] ++;
if (directed == 0)
insert_edge(g,y,x,1);
else
g->nedges ++;
}



void print_graph(graph *g)
{
int i; /* counter */
edgenode *p; /* temporary pointer */
for (i=1; i<=g->nvertices; i++) {
cout << i;
p = g->edges[i];
while (p != NULL) {
cout << p->y;
p = p->next; 
}
cout << "\n";
}
}

此外，当我在 main 之前定义函数时，我得到以下结果：

C:\Users\Garg\Desktop\try\Stack.cpp|23|error: '(' token| 之前的预期构造函数、析构函数或类型转换 C:\Users\Garg\Desktop\try\Stack.cpp|33|error: '(' token| 之前的预期构造函数、析构函数或类型转换 ||=== 构建完成：2 个错误，0 个警告 ===|

#include<iostream>
#define MAXV 1000       /* maximum number of vertices */

using namespace std;

struct node
{
int y;              /*adjacency info*/
int weight;             /* edge weight, if any */
struct node *next;      /* next edge in list */
} edgenode;


struct graph{
node *edges[MAXV+1];     /* adjacency info */
int degree[MAXV+1];             /* outdegree of each vertex */
int nvertices;          /* number of vertices in graph */
int nedges;             /* number of edges in graph */
int directed;           /* is the graph directed? */
} graph;


initialize_graph(graph *g, int directed)
{
int i;
g -> nvertices = 0;
g -> nedges = 0;
g -> directed = directed;
for (i=1; i<=MAXV; i++) g->degree[i] = 0;
for (i=1; i<=MAXV; i++) g->edges[i] = NULL;
}

read_graph(graph *g, int directed)
{
int i;
int m;
int x, y;           /* vertices in edge (x,y) */
initialize_graph(g, directed);
cout << "Enter the number of vertivces and edges";
cin >> g->nvertices;
cin >> m;
cout << "Enter the vertices for the edge and the weight of the edge";
for (i=1; i<=m; i++) {
cin >> x;
cin >> y;
insert_edge(g,x,y,directed);
}
}

insert_edge(graph *g, int x, int y, int directed)
{
struct node *p;
p = malloc(sizeof(struct node));
p->weight = NULL;
p->y = y;
p->next = g->edges[x];
g->edges[x] = p; /* insert at head of list */
g->degree[x] ++;
if (directed == 0)
insert_edge(g,y,x,1);
else
g->nedges ++; 
}



print_graph(graph *g)
{
int i; /* counter */
edgenode *p; /* temporary pointer */
for (i=1; i<=g->nvertices; i++) {
cout << i;
p = g->edges[i];
while (p != NULL) {
cout << p->y;
p = p->next;
}
cout << "\n";
}
}

int main()
{
struct graph *g = NULL;
cout << "Now reading graph";
read_graph(g, 1);
print_graph(g);
return 0;
}

有什么提示我做错了什么？

Answer 1

你有一个名为graph 的结构体和一个变量。不要那样做。

当您声明这些函数时，编译器会尝试使用该变量...

Answer 2

我认为代码

struct node
{ 
    int y;              /*adjacency info*/
    int weight;             /* edge weight, if any */
    struct node *next;      /* next edge in list */
} edgenode;

在struct 之前缺少typedef。尝试将它添加到两个结构定义中。

没有typedef，它说：这是一个结构，顺便创建一个这种类型的变量。使用 typedef，您实际上是在创建类型 edgenode 和 graph。

Answer 3

忘记声明函数的返回类型？例如，在你的最后一堆代码中initialize_graph 应该是

void initialize_graph(graph *g, int directed);

更新：

您对变量 graph 的声明会影响同名的 struct。因此，当您声明以graph* 作为参数的函数时，您指的不是类型而是变量。

另一个更新：

您声明一个指向graph 的指针并将其初始化为NULL。然后，您尝试从您的函数中取消引用此类空指针。您必须使指针指向一个有效的图形，例如通过分配给它new graph();