fopen出错的原因

[mike_33]

找了很多遍了，还是没找出错误的原因，求大神指点迷津！
运行一下代码，输入值《=80时，正常运行输出；而输入值大于80时，fopen打开出错！
想了很久，觉得可能是我对fopen还不够了解~

//Program 12.4 Page 464
#define _STDC_WANT_LIB_EXT1_ 1
#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>
#include<stdbool.h>
#include<string.h>
#define PER_LINE 8
#define MEM_PRIMES 80
struct
{
char *filename;
FILE *pfile;
unsigned long long primes[MEM_PRIMES];
size_t count;
}global={.filename="myfile.bin",.pfile=NULL,.primes={2ULL,3ULL,5ULL},.count=3};

bool is_prime(unsigned long long trial);
void list_primes(void);
void write_file(unsigned long long primes[],size_t n);

int main(void)
{
size_t total=0;
printf("How many primes do you want to print out? ");
scanf_s(" %zd",&total);
size_t num_primes=3;
unsigned long long trial=global.primes[2];
while(global.count<total)
{
trial+=2;
if(is_prime(trial))
{
if(num_primes<MEM_PRIMES-1)
{
global.primes[num_primes++]=trial;
global.count++;
}
else
{
global.primes[num_primes]=trial;
write_file(global.primes,MEM_PRIMES);
global.count++;
num_primes=0;
}
}
}
if(num_primes!=0)
write_file(global.primes,num_primes);
list_primes();
remove(global.filename);
return 0;
}
bool is_prime(unsigned long long trial)
{
size_t write_count=global.count/MEM_PRIMES;
size_t num_primes=global.count%MEM_PRIMES;
unsigned long long buf[MEM_PRIMES];
for(size_t i=0;i<num_primes;i++)
{
if(trial%global.primes[i]==0)
return false;
}
if(write_count!=0)
{
if(fopen_s(&global.pfile,global.filename,"rb"))
{
printf("Error on opening %s. Program terminated!\n",global.filename);
exit(1);
}
setvbuf(global.pfile,NULL,_IOFBF,BUFSIZ);
do
{
fread(buf,sizeof(unsigned long long),MEM_PRIMES,global.pfile);
for(size_t i=0;i<MEM_PRIMES;i++)
{
if(trial%buf[i]==0)
return false;
}
}while(!feof(global.pfile));
fclose(global.pfile);
global.pfile=NULL;
}
return true;
}

void write_file(unsigned long long primes[],size_t n)
{
if(fopen_s(&global.pfile,global.filename,"ab"))
{
printf("Error on opening %s for writing. Program terminated!\n",global.filename);
exit(1);
}
setvbuf(global.pfile,NULL,_IOFBF,BUFSIZ);
fwrite(global.primes,sizeof(unsigned long long),n,global.pfile);
fclose(global.pfile);
global.pfile=NULL;
}
void list_primes(void)
{
if(fopen_s(&global.pfile,global.filename,"rb"))
{
printf("Error on opening %s. Program terminated!\n",global.filename);
exit(1);
}
setvbuf(global.pfile,NULL,_IOFBF,BUFSIZ);
do
{
size_t n=fread(global.primes,sizeof(unsigned long long),PER_LINE,global.pfile);
for(size_t i=0;i<n;i++)
printf("%5llu",global.primes[i]);
printf("\n");
}while(!feof(global.pfile));
fclose(global.pfile);
global.pfile=NULL;
}

[赵4老师]

崩溃的时候在弹出的对话框按相应按钮进入调试，按Alt+7键查看Call Stack即“调用堆栈”里面从上到下列出的对应从里层到外层的函数调用历史。双击某一行可将光标定位到此次调用的源代码或汇编指令处，看不懂时双击下一行，直到能看懂为止。 判断是否越界访问，可以在数组的最后一个元素之后对应的地址处设置数据读写断点。如果该地址对应其它变量干扰判断，可将数组多声明一个元素，并设置数据读写断点在该多出元素对应的地址上。

#include <time.h>
#include <stdlib.h>
#include <windows.h>
int main() {
    int a,b[11];//本来是b[10]，为判断哪句越界，故意声明为b[11]

    srand((unsigned int)time(NULL));//按两次F11，等黄色右箭头指向本行时，调试、新建断点、新建数据断点，地址：&b[10]，字节计数：4，确定。
    while (1) {//按F5，会停在下面某句，此时a的值为10，b[10]已经被修改为对应0..4之一。
        b[(a=rand()%11)]=0;
        Sleep(100);
        b[(a=rand()%11)]=1;
        Sleep(100);
        b[(a=rand()%11)]=2;
        Sleep(100);
        b[(a=rand()%11)]=3;
        Sleep(100);
        b[(a=rand()%11)]=4;
        Sleep(100);
    }
    return 0;
}

[paschen]

不要凭空想是什么原因， Return value 1) If successful, returns a pointer to the new file stream. The stream is fully buffered unless filename refers to an interactive device. On error, returns a null pointer. POSIX requires that errno is set in this case. 检查errno的值来判断是什么原因 http://en.cppreference.com/w/c/io/fopen

[eastfriendwu]

确实，像这种问题，出错后，检查下errno就知道原因了，perror () 或者 strerror() 打印一下。明显问题是fopen的mode不对， "rb" ---> "ab"