Why is fgets getting stuck on carriage return \\r?

问题:

I'm new to the forum and to c in general, so please bear with me. I'm trying to write a c program that takes a text file and parses all words and characters, then saves them to an output text file. I'm using C99, Windows 7-64bit, MinGW, notepad, notepad++, and ASNI format for txt files. I've read that fgets() is better to use than fscanf for reading input because it has buffer overflow protection, so I decided to try using it, but it's having issues with some punctuation in the test file (I think it's the carriage return \r). I tried using fscanf, and aside from it skipping all of the whitespace (which I can add back in later, not concerned with that), it seems to take in all of the text just fine and print it in the output file.

Here's my test code:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>

void main(int argc, char* argv[])
{
    int limit=100, flimit=0, flimitmax=1900000000; //I stopped flimitmax short of the 2GB mark 
    char name[limit], copyname[limit];
    FILE *data, *output;

//Gets the value of a specified data file for reading   
    printf("\nPlease specify a file to format for data input.  NOTE: CHARACTERS LIMITIED TO %d\n", limit);
    fgets(name, limit, stdin); //takes input of size 'limit' and assigns it to 'name'
    size_t ln = strlen(name);   //gets the size of name[]
    if(name[ln-1]=='\n') name[ln-1]='\0'; //gets rid of newline character read in by fget
    strncpy(copyname, name, limit); //stores the value of the specified file name for use making the input and output files 
    strcat(name, ".txt"); //appends .txt file extension to the file name
    printf("\nYou chose file %s\n", name);

    data = fopen(name, "r"); //Checks to see if the specified data file exists and if it can be read
    if(data==NULL)
    {
        fprintf(stderr, "\nCan't open file %s!!!\n", name);
        exit(1);
    }

//Gets the size of the data file being worked.  Used later when the file is copied into the program using fgets.    
    fseek(data, 0, SEEK_END); // seek to end of file
    flimit = ftell(data)+1; // get current file pointer
    fseek(data, 0, SEEK_SET); // seek back to beginning of file
    if((flimit > flimitmax) || (flimit < 0))//Checks to see if flimit falls between 0 and 1.9GB.  If not, the file is larger than 1.9GB
    {
        printf("Error, max file size exceeded.  Program terminating\n");
        exit(1);
    }
    printf("File size is %d bytes\n", flimit);

//Creates a name for the output file
    strncpy(name, copyname, limit); //reassigns original value to name to make output file name
    strcat(name, "OUT.txt"); //appends OUT.txt file extension to the file name
    printf("\nOutput file is %s\n", name);

    output = fopen(name, "w"); //checks to see if the Input file exists and if it can be read
    if(output==NULL)
    {
        fprintf(stderr, "\nCan't open file %s!!!\n", name);
        exit(1);
    }

//Reads the data file and assigns values to the input and output files  

    char filein[flimit]; //I created this variable here to avoid issues of array resizing.
    //fgets attempt
    fgets(filein, flimit, data); //scans the whole datafile and stores it in the char array.

    printf("\n%s\n", filein);
    fprintf(output, filein);

    memset(&filein[0], 0, sizeof(filein)); //clears the filein array

    fseek(data, 0, SEEK_SET); // seek back to beginning of file 
    //fscanf attempt
    while(fscanf(data, "%s", &filein)!=EOF)
    {
        printf("\n%s\n", filein);
        fprintf(output, filein);
    }

//Closes the files and ends the program
    printf("\nDONE!!!\n");
    fclose(data);
    fclose(output);
}

Here's the text I use in the data file:

Things/Words and punctuation:  The Test

This is a test (mostly to see if this program is working).

Here's the output I get from the output file:

Things/Words and punctuation:  The Test
Things/Wordsandpunctuation:TheTestThisisatest(mostlytoseeifthisprogramisworking).

Why is fgets() getting hung-up? It gets the first line just fine, then it gets stuck.

Thanks in advance for taking the time to look at this. If you have any other recommendations for my code, feel free to let me know.

回答1:

"The fgets function will stop reading when flimit characters are read, the first new-line character is encountered in filein, or at the end-of-file, whichever comes first."

Your fgets() encounters a new-line character and halts. That's why you need to use a while loop to keep your code running until you reach the end of the file. Upon successful completion, fgets() returns a stream. If this stream is at end-of-file, fgets() returns a null pointer.

The following code block solves your problem,

...

    while(fgets(filein,flimit,data) != NULL)
    {
        printf("%s\n",filein);
        fprintf(output,filein);
    }

...

The following link explains the correct usage of fgets function with examples.

Reference: http://pubs.opengroup.org/onlinepubs/009695399/functions/fgets.html

Hope it helps,