string from file C

Question

I'm reading a string from a file and then, trying to add zeros to the string till it reach 100, and then I'm printing the string, but I don't know what's wrong, I've tried more than one approach , but they all seems not to work.

int main(int argc, char *argv[])
{
    if (argc != 2 ){
        fprintf(stderr, "usage: server filename \n");
        exit(1);
    }
    FILE *file = fopen(argv[1], "r");
    if (file==0)
    {
        printf("file couldn't be opened\n");
        exit(1);
    } 
    int i;
    char str1[100];
    //char str2[100];
    //memset(str2,0,sizeof(str2));
     //for(i = 0; i < 100; i++)
         // fprintf(stdout, "str2[%u]: %u\n",i,str2[i]);

    while (fscanf(file, "%s", str1) != EOF) 
    {
        for(i=13 ; i < 100; i++)
            str1[i]=0;


    }

         for(i = 0; i < 100; i++)
         fprintf(stdout, "str1[%u]: %u\n",i,str1[i]);

    return 0;
}

but I print it I got

str1[0]: 119
str1[1]: 111
str1[2]: 114
str1[3]: 108
str1[4]: 100
str1[5]: 0
str1[6]: 0
str1[7]: 0
up till 99

I don't understand this although there is a string in the file "hello" and then I've tried this

int main(int argc, char *argv[])
{
    if (argc != 2 ){
        fprintf(stderr, "usage: server filename \n");
        exit(1);
    }
    FILE *file = fopen(argv[1], "r");
    if (file==0)
    {
        printf("file couldn't be opened\n");
        exit(1);
    } 
    int i;
    char str1[12];
    char str2[100];
    memset(str2,0,sizeof(str2));
     //for(i = 0; i < 100; i++)
         // fprintf(stdout, "str2[%u]: %u\n",i,str2[i]);

    while (fscanf(file, "%s", str1) != EOF) 
    {

     strcpy(str2,str1);

    }

         for(i = 0; i < 100; i++)
         fprintf(stdout, "str2[%u]: %u\n",i,str2[i]);

    return 0;
}

and I gave me the exact same result as the first one, so I don't understand what is happening here, and why I'm getting these results. I'll be grateful if you can explain what I'm doing wrong here. Thanks in advance.

Answer 1

In the last code snippet, you shouldn't do:

memset(str2,0,sizeof(str2));

but instead:

memset(str2,0,sizeof(char) * 100);

Check this link on sizeof: http://en.wikibooks.org/wiki/C_Programming/Pointers_and_arrays#sizeof

Answer 2

A lot of wrong things here.

Most obvious one to me is that you're printing each character as %u, which is unsigned int. You should print each character as char, that is, %c.

Second, as pointed out by fableal, your memset() is also wrong. Using sizeof(str2) means size of str2, which is a pointer, which, in 32-bit architectures, will be 32 bits. This is obviously not what you want.

Answer 3

The reason you are not seeing the characters is because the printf is printing integers. Change it to %c:

fprintf(stdout, "str2[%u]: %c\n",i,str2[i]);

Answer 4

This:

memset(str2,0,sizeof(str2));

is not needed, since this:

while (fscanf(file, "%s", str1) != EOF) 
{
 strcpy(str2,str1);
}

overwrites str2 with str1 for each iteration. This means the previous string is thrown away. It's possible that you meant strcat(), in which case you should have str2[0] = '\0';` before the loop.

Answer 5

Your goal, if I understand correctly, is to have a character array which will have the single line from a file in it, and 0's besides that. For example:

File:

hello

Array result:

[h][e][l][l][o][0][0][0]...

So the easy way to do that is start by init your array to 0's, then read the line out:

char str1[100] = {'0'};
fgets(str1, 100, file); 

To print them you can print it like the string it is:

printf("%s\n", str1); 

But keep in mind you set the whole thing to 0 (null terminators) so you'll only see "hello". If you print with decimals as you were doing:

for(i=0; i<100; i++)
  printf("%d ", str1[i]);

You'll see hello in ASCII followed by the 0's

104 101 108 108 111 10 0 0 0 0 0 0 0 0 0...