我使用压缩的稀疏行数据结构编写了一个用于在C中首次搜索的代码。该代码似乎适用于一个图形，但返回另一个图形文件的错误。它对此文件效果很好，但是对于C编程的新文件会引发错误，我找不到问题的原因，并且会感谢任何帮助
我尝试检查段循环的条件。当代码挂起并返回错误时，循环的条件是正确的。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;
}
您将int heads[m];用作 m = 108744的int的VLA（以及其他4个VLA，您分配了2950整数）可能会导致stackoverflow ...（这将是编译器，OS，OS，OS和内存模型依赖）。要解决问题，请更改CSRgraph，以使成员heads和offsets是指示器，然后根据文件的第一行读取的数字动态分配存储，例如，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在offsets上使用将其初始化为所有零，因为您以后比较p < g.offsets[curr+1]）
将其完全放置，您可以做：
#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：避免硬编码文件名，例如fopen("filename.graph","r")，main()进行参数，使用它们将文件名作为第一个参数将作为程序的第一个参数传递给您的程序[并且您可以默认情况下从stdin读取，如果没有参数为提供]）
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文件一起使用。