由于strcpy（）造成的分段错误

Question

why am i getting segmentation fault in strcpy()?

the program gets compiled without any problem but i am getting a segmentation fault because of strcpy please suggest me a way out.

struct obj
{
    char objcode[100];
}o[10];

int main()
{
    char buffer[500],statement[50][50];/*storing each statement*/
    int i=0,fd;
    int j=0,k=0;
    char *tok;
    fd=open("objectprogram.txt",O_RDONLY);
    const ssize_t r=read(fd,buffer,500);
    buffer[r]='\0';
    char *sta;
    sta=strtok(buffer,"\n");
    while(sta!=NULL)
    {
        strcpy(statement[i],sta);
        i++;
        sta=strtok(NULL,"\n");
    }   
    for(j=1;j<i-1;j++)
    {
        tok=strtok(statement[j],"^");
        tok=strtok(NULL,"^"); 
        tok=strtok(NULL,"^");
        while(tok!=NULL)
        {
            tok=strtok(NULL,"^");
            strcpy(o[k].objcode,tok);
        }

    }
}

Answer 1

Your check for tok==NULL in the while loop happens after the call to strcpy , not before. You're trying to copy a NULL pointer.

Whenever you get a segmentation fault, the first thing to look for is the possibility of a NULL pointer.

Answer 2

In this code:

                    while(tok!=NULL)
                    {
                        tok=strtok(NULL,"^");
                        strcpy(o[k].objcode,tok);
                    }

You check for tok 's validity before entering the loop but not after it gets changed by strtok() .

A debugger should have been able to identify exactly which line of code had the problem, and from within the debugger you could see if the value of tok is okay or not at the time strcpy() gets called.

Answer 3

strcpy is not safe in terms of array size, use strncpy instead!!

ie if you get more data in your input, you will overflow your statement[i].