如何多次读取文件C

Question

I am trying to store a list of words from a file into a char* . I am not to assume a max number of lines or a max number of characters. So to combat this, I decided to do a run through of the .txt file to find the number of lines and the maximum number of characters so I can allocate memory to char * list.

However, when I used GDB to debug my program, it skips over the second runthough of the file to store in the words. Why is it doing this and how do I fix it? Thanks!

void readFile(int argc, char** argv)
{
    FILE *myFile;
    char** list;
    char c;
    int wordLine = 0, counter = 0, i;
    int maxNumberOfChars = 0, numberOfLines = 0, numberOfChars = 0;

    myFile = fopen(argv[1], "r");

    if(!myFile)
    {
        printf("No such file or directory\n");
        exit(EXIT_FAILURE);  
    }

    while((c = fgetc(myFile)) !=EOF)
    {
        numberOfChars++;
        if(c == '\n')
        {
            if(maxNumberOfChars < numberOfChars)
                maxNumberOfChars += numberOfChars + 1;

            numberOfLines++;
        }
    }

    fseek(myFile, 0, SEEK_SET);

    list = malloc(sizeof(char*)*numberOfLines);

    for(i = 0; i < wordLine ; i++)
        list[i] = malloc(sizeof(char)*maxNumberOfChars);


    while((c = fgetc(myFile)) != EOF)
    {
        if(c == '\n' && counter > 0)
        {
            list[wordLine][counter] = '\0';
            wordLine++;
            counter = 0;
        }
        else if(c != '\n')
        {
            list[wordLine][counter] = c;
            counter++;
        }
    } 
    fclose(myFile);
}

Answer 1

You need to use fseek to reset the read-pointer of the file before your second loop.

Add something like this

fseek(myFile, 0, SEEK_SET);

or

rewind(myFile);

thanks to @ThomasPadron-McCarthy.

Answer 2

1st of all, your technique is bad because it is very slow. You can just allocate some memory and then use realloc if you need more.

2nd: you can use stat() on a file to know the size. You won't know the number of lines in it but it could be useful.

3rd: you can use fseek() to move the cursor back to the beginning of the file, and in general to any position within the file.

Answer 3

再次读取之前，请使用rewind（myFile）。

rewind(myFile)

Answer 4

but you don't need to read the whole file just to find out the number of chars. You can use this structure

struct stat file_stat;
fstat(file_id, &file_stat);
int size_to_read = file_stat.st_size - 1;

you don need to know the number of lines, because you can can use realloc on line:

list=realloc(list,(sizeof(char*)));