adding characters from text file into an array

Question

I am new to C and am trying to complete an assignment. The program should take a file name as an command line argument, then print the file contents. My program prints jumbled up text instead of the actual text in file.

I have searched all over the Internet for examples/answers to my problem and remain stuck!

What am I doing wrong?. If it can be helped, please modify my code instead of writing new code so that I will have an easier time understanding.

int main()
{
    char fileName[20];
    int *buffer;
    int size;

    // ask for file name and take input.
    printf("Enter file name: ");            
    scanf("%s", fileName);

    // open file in read mode.
    FILE *fp;
    fp = fopen(fileName, "r");          

    // If no file, show error.
    if(fp == NULL)                  
    {
        printf("Error: Can't open file.\n");        
        return 1;
    }

    // count characters in file with fseek and put into size, then move the
    // position of the file back to the beginning.
    fseek(fp, 0, SEEK_END);
    size = ftell(fp);
    rewind(fp);

    // allocate buffer and read file into buffer.
    buffer = malloc(size+1);
    fread(buffer, 1, size, fp);

    // close the file.
    fclose(fp);

    // for loop reading array one character at a time.
    for(int x = 0; x < size; x++)
    {               
        printf("%c", buffer[x]);
    }

    return 0;
}

Always be wary of buffer overflows. A 20 character buffer is crazy tiny. If you're having a malfunction with compiled code, open your debugger. — tadman
– tadman, Commented Sep 14, 2017 at 19:28
x < size : Use return value of fread instead of size. The number of actually read characters may be different. — BLUEPIXY
– BLUEPIXY, Commented Sep 15, 2017 at 2:09

Stephan Lechner · Accepted Answer · 2017-09-14 19:36:10Z

2

You are using the wrong datatype for reading in characters, i.e. you use int *buffer, but you should use char *buffer.

When using int *buffer, an access like printf("%c",buffer[x]) will access your buffer as an array of integers; an integer is probably of size 4, such that buffer[1] addresses the 4th byte in the buffer, buffer[2] the 8th and so forth... Hence, you will read out elements that are not contained in the file any more, actually exceeding array bounds (leading to garbage or something else).

edited Sep 14, 2017 at 19:36

answered Sep 14, 2017 at 19:30

Stephan Lechner

35.2k4 gold badges38 silver badges59 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

adding characters from text file into an array

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related