C Programming - Structures, Unions, Enums - Discussion
Discussion Forum : Structures, Unions, Enums - Yes / No Questions (Q.No. 1)
1.
If the following structure is written to a file using fwrite(), can fread() read it back successfully?
struct emp
{
char *n;
int age;
};
struct emp e={"IndiaBIX", 15};
FILE *fp;
fwrite(&e, sizeof(e), 1, fp);
Answer: Option
Explanation:
Since the structure contain a char pointer while writing the structure to the disk using fwrite() only the value stored in pointer n will get written. so fread() fails to read.
Discussion:
8 comments Page 1 of 1.
Anil kumar arikicherla said:
9 months ago
I think here is a syntax error;
fwrite(&e, sizeof(e), 1, fp);
insted; fwrite(&e, sizeof(e), fp); =>this would be the correct one.
fwrite(&e, sizeof(e), 1, fp);
insted; fwrite(&e, sizeof(e), fp); =>this would be the correct one.
SHI said:
7 years ago
I agree @Tonyg. Option B is correct.
Zdd said:
7 years ago
I agree with @Tonyg.
In another program, we cannot use fread() to read it back.
So, Option B is correct.
In another program, we cannot use fread() to read it back.
So, Option B is correct.
Selluboy said:
8 years ago
Yes. As Roman said, Option A is correct. We can read the contents of structure that is written through one file using another program file.
TonyG said:
9 years ago
Option B is correct.
What Roman points out above is correct, but the question is ambiguous.
The question is referring to a separate program reading it back.
When a separate program is reading it back with an freed and will only receive the value of the pointer. N will not point to anything useful.
What Roman points out above is correct, but the question is ambiguous.
The question is referring to a separate program reading it back.
When a separate program is reading it back with an freed and will only receive the value of the pointer. N will not point to anything useful.
Roman said:
1 decade ago
Option A is right. The structure contain pointer. Not value, but pointer itself will be written/read. Verified with gcc.
fp = fopen("my.bin", "w");
fwrite(&ew, sizeof(ew), 1, fp);
printf(" ew %s, %d\n", ew.n, ew.age);
fclose(fp);
fp = fopen("my.bin", "r");
fread(&ew, sizeof(ew), 1, fp);
fclose(fp);
printf(" ew %s, %d\n", ew.n, ew.age);
Output:
ew IndiaBIX, 15
ew IndiaBIX, 15
fp = fopen("my.bin", "w");
fwrite(&ew, sizeof(ew), 1, fp);
printf(" ew %s, %d\n", ew.n, ew.age);
fclose(fp);
fp = fopen("my.bin", "r");
fread(&ew, sizeof(ew), 1, fp);
fclose(fp);
printf(" ew %s, %d\n", ew.n, ew.age);
Output:
ew IndiaBIX, 15
ew IndiaBIX, 15
Swathireddy said:
1 decade ago
Explain about where we use fwrite(), fread().
Ann said:
1 decade ago
Please explain the concept.
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