我使用压缩的稀疏行数据结构在C中编写了广度优先搜索的代码。该代码对于一个图形似乎运行良好，但是对于另一个图形文件则返回错误。它对this file来说效果很好，但对this file却引发了错误，我是C编程新手，我找不到问题的原因，将不胜感激
我尝试检查while循环的条件。当代码挂断并返回错误时，循环的条件为true。我正在使用mingw编译器在CodeBlocks 16.01上运行此代码。
#include <stdio.h>
#include <stdlib.h>
// Declaring a struct type to hold
int main(){
int n, m, counter, current, x, src, dst;
n=0, m=0, counter = 0, current =0, src = 0, dst = 0;
FILE *fp; //create a pointer to the file directory
fp = fopen("filename.graph","r"); //set the directory pointer to the path of the text file containing graph data
if ((fp == NULL)){ perror("Error, no such file exists \n"); exit(1);}
//If file not found, print error message and exit the program
else
{
fscanf(fp,"%d %d", &n,&m); //read first line of text file to get number of vertices and edges in graph
struct CSRgraph //Create CSR data structure
{
int heads[m]; //Stores heads of edges
int offsets[n+1]; //Stores information on the number of edges leaving each node
};
struct CSRgraph g; //Create an instance of the CSR graph data structure
g.offsets[0] = 0; //Set the initial offset value to 0
g.offsets[n] = m; //Set the offset value of 'phantom' node to the number of edges in graph
for(x=0;x<m;x++) //iterate over all lines containing edge information in text file
//Read file and create CSR data structure from information in text file
{
fscanf(fp,"%d %d",&src,&dst); //read source and head information from file
g.heads[x] = dst; //assign head information to the next available slot in data structure
if (src < n+1) //Check that node is valid
{
if (src == current) //check that current edge originates from same source as previous edge
{
counter++; //increment counter for the number of edges that originate from current source
}
else //Current edge does not originate from previous source. New source node encountered
{
g.offsets[src] = counter + g.offsets[src -1]; //Update offset value for previous source
counter = 1; //restart edge origin counter
current = src ; //set current to current source
}
}
}
fclose(fp); //Close file after use
int Discovered[n],Queue[n+1],Explored[n], *front_ptr,*end_ptr,*exp_ptr;
front_ptr = Queue; //Initialize the front pointer to the Queue array
end_ptr = Queue; //Initialize the end pointer to the Queue array
exp_ptr = Explored; //Initialize the explored pointer to the Explored array
for (x=0;x<n;x++)
{
Discovered[x] = 0; //An array to track discovered nodes. Not necessarily explored, but nodes that have showed up previously
}
// Advance the pointers in the direction you want
*end_ptr = 0; //setting the first element in the queue as the node 0
end_ptr++; //advancing the end pointer to the next available array spot
Discovered[0] = 1;
while (front_ptr != end_ptr)
{ //Queue is empty if front pointer is the same as end pointer
int p,curr;
curr = *front_ptr; //grab the front of the queue and set it as current node
front_ptr++; //equivalent to removing from element and pushing the next node in line to the front
*exp_ptr = curr; //set current node to explored
exp_ptr++; //advance the explored pointer one step
for (p = g.offsets[curr]; p < g.offsets[curr+1]; p++)
//iterate over all neighbors of current node
{
if (Discovered[g.heads[p]] == 0)
//if node is not already discovered, set it to discovered, add it to queue and advanced the end pointer of queue one step
{
Discovered[g.heads[p]] = 1;
*end_ptr = g.heads[p];
end_ptr++;
}
}
}
}
return 0;
}
答案 0 :(得分：0)
您将int heads[m];用作m = 108744的int的VLA（以及您分配的2950整数的其他4个VLA）可能会引起StackOverflow ...（这将取决于编译器，操作系统和内存模型）。要解决该问题，请更改CSRgraph，以使成员heads和offsets是指针，然后根据从文件第一行读取的数字（例如
typedef struct { /* typdef for convenience */
int *heads,
*offsets;
} CSRgraph_t;
int main (int argc, char **argv) {
CSRgraph_t g; /* declare instance of struct */
...
/* allocate/validate g.heads & g.offsets */
if (!(g.heads = malloc (m * sizeof *g.heads))) {
perror ("malloc-g.heads");
return 1;
}
/* calloc used to zero g.offsets */
if (!(g.offsets = calloc ((n + 1), sizeof *g.offsets))) {
perror ("malloc-g.offsets");
return 1;
}
g.offsets[0] = 0;
g.offsets[n] = m;
...
（注意： calloc上使用offsets将其初始化为全零，以便您稍后比较p < g.offsets[curr+1]）
完全将其放入，您可以这样做：
#include <stdio.h>
#include <stdlib.h>
typedef struct { /* typdef for convenience */
int *heads,
*offsets;
} CSRgraph_t;
int main (int argc, char **argv) {
CSRgraph_t g; /* declare instance of struct */
int n, m, counter, current;
n = m = counter = current = 0;
/* use filename provided as 1st argument (stdin by default) */
FILE *fp = argc > 1 ? fopen (argv[1], "r") : stdin;
if (!fp) { /* validate file open for reading */
perror ("file open failed");
return 1;
}
if (fscanf (fp, "%d %d", &n, &m) != 2) { /* validate EVERY read */
fputs ("error: invalid format n, m.\n", stderr);
return 1;
}
/* allocate/validate g.heads & g.offsets */
if (!(g.heads = malloc (m * sizeof *g.heads))) {
perror ("malloc-g.heads");
return 1;
}
/* calloc used to zero g.offsets */
if (!(g.offsets = calloc ((n + 1), sizeof *g.offsets))) {
perror ("malloc-g.offsets");
return 1;
}
g.offsets[0] = 0;
g.offsets[n] = m;
for (int x = 0; x < m; x++) {
int src; /* src is only needed within scope of loop */
if (fscanf (fp, "%d %d", &src, &g.heads[x]) != 2) {
fprintf (stderr, "error: invalid format - line %d.\n", x);
}
if (src < n+1) {
if (src == current)
counter++;
}
else {
g.offsets[src] = counter + g.offsets[src -1];
counter = 1; /* restart edge origin counter */
current = src; /* set current to current source */
}
}
if (fp != stdin) fclose (fp); /* close file if not stdin */
int Discovered[n], Queue[n+1], Explored[n],
*front_ptr, *end_ptr, *exp_ptr;
front_ptr = Queue; /* front pointer to the Queue array */
end_ptr = Queue; /* end pointer to the Queue array */
exp_ptr = Explored; /* explored pointer to the Explored array */
for (int x = 0; x < n; x++)
Discovered[x] = 0;
/* Advance the pointers in the direction you want */
*end_ptr = 0;
end_ptr++;
Discovered[0] = 1;
while (front_ptr != end_ptr) {
int curr = *front_ptr;
front_ptr++;
*exp_ptr = curr;
exp_ptr++;
for (int p = g.offsets[curr]; p < g.offsets[curr+1]; p++) {
if (Discovered[g.heads[p]] == 0) {
Discovered[g.heads[p]] = 1;
*end_ptr = g.heads[p];
end_ptr++;
}
}
}
free (g.heads);
free (g.offsets);
return 0;
}
（注意：避免对文件名进行硬编码，例如fopen("filename.graph","r")，main()接受参数，使用它们将文件名作为第一个参数传递给程序[您可以阅读如果没有提供参数，则默认为stdin。]
内存使用/错误检查
$ valgrind ./bin/readgraphsfile ~/tmp/graphfile/large.graph
==17345== Memcheck, a memory error detector
==17345== Copyright (C) 2002-2015, and GNU GPL'd, by Julian Seward et al.
==17345== Using Valgrind-3.12.0 and LibVEX; rerun with -h for copyright info
==17345== Command: ./bin/readgraphsfile ~/tmp/graphfile/large.graph
==17345==
==17345==
==17345== HEAP SUMMARY:
==17345== in use at exit: 0 bytes in 0 blocks
==17345== total heap usage: 3 allocs, 3 frees, 447,332 bytes allocated
==17345==
==17345== All heap blocks were freed -- no leaks are possible
==17345==
==17345== For counts of detected and suppressed errors, rerun with: -v
==17345== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
它可以与您的large.graph文件一起正常工作。