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#include<stdio.h>int main()
{FILE *file;
char sentence[50];
int i;file = fopen("sentence.txt", "w+");
/* we create a file for reading and writing */if(file==NULL) {
printf("Error: can't create file.\n");return 1;
}else {
printf("File created successfully.\n");printf("Enter a sentence less than 50 characters: ");
gets(sentence);for(i=0 ; sentence[i] ; i++) {fputc(sentence[i], file);}
rewind(file); /* reset the file pointer's position */
printf("Contents of the file: \n\n");while(!feof(file)) {
printf("%c", fgetc(file));}
printf("\n");fclose(file);
return 0;}
} Output depends on what you entered. First of all, we stored the inputted sentence in a char array, since we're writing to a file one character at a time it'd be useful to detect for the null character. Recall that the null character, \0, returns 0, so putting sentence[i] in the condition part of the for loop iterates until the null character is met.
Then we call rewind, which takes the file pointer to the beginning of the file, so we can read from it. In the while loop we print the contents a character at a time, until we reach the end of the file - determined by using the feof function.
Note that it is essential to have the include file stdio.h referenced at the top of your program in order to use any of these functions: fscanf(), fgets(), fgetc(), fflush(), fprintf(), fputs(), fputc(), feof(), fseek() và rewind().
When a function returns EOF (or, occasionally, 0 or NULL, as in the case of fread and fgets respectively), we commonly say that we have reached “end of file” but it turns out that it's also possible that there's been some kind of I/O error. When you want to distinguish between end-of-file and error, you can do so with the feof and ferror functions. feof(fp) returns nonzero (that is, “true”) if end-of-file has been reached on the file pointer fp, and ferror(fp) returns nonzero if there has been an error.
Notice feof returns nonzero if end-of-file has been reached. It does not tell you that the next attempt to read from the stream will reach end-of-file, but rather that the previous attempt (by some other function) already did. (If you know Pascal, you may notice that the end-of-file detection situation in C is therefore quite different from Pascal.) Therefore, you would never write a loop like
while(!feof(fp))
fgets(line, max, fp);
Instead, check the return value of the input function directly:
while(fgets(line, max, fp) != NULL)
With a very few possible exceptions, you don't use feof to detect end-of-file; you use feof or ferror to distinguish between end-of-file and error. (You can also use ferror to diagnose error conditions on output files.)
Since the end-of-file and error conditions tend to persist on a stream, it's sometimes necessary to clear (reset) them, which you can do with clearerr(FILE *fp) .
What should your program do if it detects an I/O error? Certainly, it cannot continue as usual; usually, it will print an error message. The simplest error messages are of the form
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