fscanf（）seg fault程序接收信号EXC_BAD_ACCESS

Question

  16 char* input = (char*) argv[1]; 17 FILE *fp = fopen (input, "r"); 18 if( fp == NULL) 19 { 20 printf(" reading input file failed"); 21 return 0; 22 } 23 fseek(fp,0,SEEK_END); 24 int file_size = ftell(fp); 29 rewind(fp); 30 int i; 31 int totalRun; 32 char * temp; 33 char* model; 34 char* example; 36 fscanf(fp,"%d",&totalRun); 37 fscanf(fp,"%s",model); 

Above is my code I get this error at line 37 "fscanf(fp,"%s".model)"

Program received signal EXC_BAD_ACCESS, Could not access memory. Reason: KERN_PROTECTION_FAILURE at address: 0x00007fff5fc00730 0x00007fff8db20bcb in __svfscanf_l ()

What can cause this ?? I looked into *fp in gdb. before reading totalRun _offset = 0 and after reading _offset = 4096. content of totalRun was correct ("3"). I only read one line and why is offset 4096? Also what is _blksize referring to in FILE.

Thank you

Answer 1

You need to allocate memory for model , it is an uninitialised pointer. Also ensure fscanf() does not read beyond the array assigned to model . If model does not need to by dynamically allocated then just use a local array. For example:

char model[1024];
if (1 == fscanf(fp, "%1023s", model))
{
}

Always check the return value of fscanf() , which returns the number of successful assignments, otherwise the program will be processing uninitialised variables if the call to fscanf() fails.

Answer 2

The variable model is not initalized. You must allocated memory for it before it can be used in the fscanf() method. You can do in two ways:

1. Statically - char model[1024];
2. Dynamically - char * model = (char*) malloc(1024); Don't forget to use free() to deallocate the buffer once you are done.