从文件中打印错误的值

Question

I tried the following code to write a structure to a file:

#include<stdio.h>

struct record
{
char name[80];
int roll;
};

int main( )
{
    FILE* p=NULL;
    int length=0;
    char* file="abcd.txt";
    struct record r1={"abcd",55};
    p=fopen(file,"w");
    if (p==NULL)    {
        printf("Error in opening file");
    }
    length=sizeof(r1);
    fwrite(&r1,length,1,p);
    fclose(p);
    printf("Written successfully\n");
    free(r1);
}

When I try to read the following file using :

#include<stdio.h>

main( )
{
    int c;
    FILE* p=NULL;
    p=fopen("abcd.txt","r");
    if (p)  {
        while ((c=getc(p)) != EOF)
            putchar (c);
        fclose(p);
    }
}

When I run the last program,the values printed are:

abcd 7

Well first field "abcd" is rightly printed,but the next value printed is 7,though I tried to write 55 in the file.What is going wrong?

Answer 1

It's because you read the integer value 55 as a character , and in the ASCII alphabet the value 55 is the same as the character '7' .

You need to read the structure the same way you write it, using fread .