我正在尝试使用名为“Topoligical Sorting”的算法来绘制图形。
为了使用它，我创建了两个数据结构：图形和堆栈。两者都是分开编写的。
我正在尝试在文件graph.c中使用堆栈数据结构（以及诸如push和pop之类的操作）。为此，我写了：
#include "stack.h"
在graph.c中，当我编译它时，没有错误。
嗯，当我在graph.c中创建堆栈s1时没有编译错误（参见下面的代码）：
Stack *s1 = init(); //Creates a stack s1
当我尝试使用堆栈的另一个操作（如push和pop）时出现问题。例如，如果我写：
push(3,s1);
尝试编译它，出现以下错误：
graph.c: In function `DIGRAPHdfs':
graph.c:71: parse error before `int'
graph.c:73: `v' undeclared (first use in this function)
graph.c:73: (Each undeclared identifier is reported only once
graph.c:73: for each function it appears in.)
当我尝试使用pop函数时出现同样的错误。
为什么我会收到此错误编译？
（请参阅此代码中的函数Digraphdfs，出现错误）
#include<stdio.h>
#include<stdlib.h>
#include "graph.h"
#include "stack.h"
#define maxV 10000
static int count, pre[maxV],lbl[maxV];
struct digraph {
int V;
int A;
int **adj;
};
//Cria a matriz de adjacências (utilizando a técnica de vetor de ponteiros)
int **MATRIXint( int r, int c, int val) {
Vertex i,j;
int **m = malloc(r*sizeof(int*));
for (i = 0; i < r; i++)
m[i] = malloc(c*sizeof(int));
for (i = 0; i < r; i++)
for (j = 0; j < c; j++)
m[i][j] = val;
return m;
}
//Cria o digrafo com V vertices e V arcos
Digraph DIGRAPHinit(int V){
Digraph G = malloc(sizeof *G);
G->V = V;
G->A = 0;
G->adj = MATRIXint(V,V,0);
return G;
}
//Insere o arco entre v e w
void DIGRAPHinsertA( Digraph G, Vertex v, Vertex w) {
if (G->adj[v][w] == 0)
{
G->adj[v][w] = 1;
G->A++;
}
}
//Remove o arco entre v e w
void DIGRAPHremoveA( Digraph G, Vertex v, Vertex w){
if (G->adj[v][w] == 1){
G->adj[v][w] = 0;
G->A--;
}
}
void DIGRAPHshow(Digraph G){
Vertex v,w;
for (v = 0; v < G->V; v++){
printf("%2d:", v);
for (w = 0; w < G->V; w++)
if (G->adj[v][w] == 1)
printf(" %2d", w);
printf("\n");
}
}
void DIGRAPHdfs( Digraph G) {
Stack *s1 = init(); //There's no error when I create a stack
push(3,s1); //I get a compilation error when I try to use the push function (The same for "pop").
Vertex v;
count = 0;
for (v = 0; v < G->V; v++)
pre[v] = -1;
for (v = 0; v < G->V; v++)
if(pre[v] == -1)
dfsR(G,v);
for (v = 0; v< G->V;v++)
printf("%d ",pre[v]);
printf("\n");
}
void dfsR(Digraph G, Vertex v) {
Vertex w;
pre[v] = count++;
for(w = 0; w < G->V; w++)
if(G->adj[v][w] != 0 && pre[w] == -1)
dfsR(G,w);
}
int DIGRAPHreach( Digraph G, Vertex s, Vertex t) {
Vertex w;
for (w = 0; w< G->V; w++)
lbl[w] = 0;
reachR(G,s);
if (lbl[t] == 0) return 0;
else return 1;
}
void reachR (Digraph G, Vertex v) {
Vertex w;
lbl[v] = 1;
for (w = 0; w < G->V; w++)
if(G->adj[v][w] == 1 && lbl[w] == 0)
reachR(G,w);
}
#define Vertex int
typedef struct digraph *Digraph;
Digraph DIGRAPHinit(int V);
int **MATRIXint(int r, int c, int val);
void DIGRAPHinsertA(Digraph G, Vertex v, Vertex w);
void DIGRAPHremoveA(Digraph G, Vertex v, Vertex w);
void DIGRAPHshow(Digraph G);
void DIGRAPHdfs( Digraph G);
void dfsR(Digraph G, Vertex v);
void reachR (Digraph G, Vertex v);
int DIGRAPHreach( Digraph G, Vertex s, Vertex t);
#include<stdio.h>
#include<stdlib.h>
#include "stack.h"
#define N 5
struct stack {
int n; //The quantity of elements of the stack
int vector[5]; //The stacks as a vector.
};
//Initialization of the stack
Stack* init(){
Stack *s;
s = (Stack*)malloc(sizeof(Stack));
if (s == NULL){
printf("FATAL ERROR!\n");
exit(1);
}
s->n = 0;
return s;
}
//Push Operation
void push(int q,Stack*s){
//Checks stack overflow
if (s->n == N){
printf("Stack Overflow!\n");
exit(1);
}
s->vector[s->n] = q;
s->n++;
}
int pop(Stack*s){
int v;
if (s->n == 0){
printf("There's no element in the stack!\n");
exit(2);
}
s->n--;
v = s->vector[s->n];
return v;
}
void print_stack(Stack*s){
int i;
for(i = 0; i<s->n; i++){
printf("vector[%d] = %d \n",i, s->vector[i]);
}
}
typedef struct stack Stack;
Stack* init();
void push(int q,Stack*s);
void print_stack(Stack*s);
int pop(Stack*s);
答案 0 :(得分：4)
您的编译器似乎是ANSI C编译器。在ANSI C中，所有变量声明必须位于块的顶部。变量声明之间不允许声明。要解决您的错误，请将push()调用移至v声明
void DIGRAPHdfs( Digraph G) {
Stack *s1 = init(); //There's no error when I create a stack
Vertex v;
push(3,s1); //I get a compilation error when I try to use the push function (The same for "pop").
count = 0;
for (v = 0; v < G->V; v++)
pre[v] = -1;
for (v = 0; v < G->V; v++)
if(pre[v] == -1)
dfsR(G,v);
for (v = 0; v< G->V;v++)
printf("%d ",pre[v]);
printf("\n");
}
答案 1 :(得分：2)
一开始，C只允许在块的开头声明变量。您可以更改代码：
void DIGRAPHdfs( Digraph G) {
Stack *s1 = init(); //There's no error when I create a stack
Vertex v; // Declaration moved to before any statements.
push(3,s1);
或者您可以更改编译以符合以后的标准。对于gcc，默认使用c90标准。如果您添加标记-std=c99 gcc将使用c99标准。如果您使用其他编译器，请查看相应编译器选项的文档。