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cstringtextinputprinting
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Reputation: 531

C Programming — get multiple words in string

I am trying to get a full sentence eg. "This is a sentence." to be stored in the global variable string named 'global'. It will then print out the sentence back out. However after entering my input, I can only get the first word of the sentence printed (This). Anyone got any ideas? 

#include <string.h>

char** global;

int main () {

    printf("Please Enter Text: \n");
    scanf("%s", &global);

    printf("%s", &global);


    return 0;
}

Upvotes: 3

Views: 11928

Answers (3)

Arpit
Arpit

Reputation: 12797

The char** global should be char* global only.

& with printf is not required.

You need to use fgets(var_name,no_of_chars,FILE*) in place of scanf.

fgets(global,100,stdin); //where global is char global[100];

Example :

Use of gets is more serious then i was thinking. So it's no longer recommended.

A Better one 

char global[100];    
int main () {
    printf("Please Enter Text: \n");
    if(fgets(global,50,stdin)) //It will take Maximum 50 chars. So no buffer overflow. 
    fputs(global,stdout);
    return 0;
}

Upvotes: 4

Jonathan Leffler
Jonathan Leffler

Reputation: 753665

Your variable char **global; is a disaster zone. It is a null pointer. It must be made to point to some valid data before it can be used. It is a double pointer, in fact, so you have to make space available like this:

char array[1000];
char *pointer = array;
char **global = &pointer;

Now you could safely use global[0].

Inside the function, you pass &global to scanf(); that is a char ***. Being a 'Three-Star Programmer' is not a good thing, especially when you do it by accident and not by design.

You include the header <string.h> but don't use any of its functions. You do use functions from <stdio.h> and you don't include that. Technically, you invoke undefined behaviour by using the variadic functions printf() and scanf() without a function prototype in scope. The compiler is entitled to be told about functions that take a variable number of arguments (that's what 'variadic' means), and is entitled to miscompile code where it is not told that the function is variadic.

Assuming you really do need a global variable at all (they're generally not a good idea and you should avoid using them as much as possible), then you could reasonably write:

#include <stdio.h>

char global[1000];

int main(void)
{
    printf("Please Enter Text: ");
    if (scanf("%s", global) == 1)
        printf("%s\n", global);
    return 0;
}

This is at least sound code, but it still has your original problem that it reads only one word, not a whole line.

Forget that gets() exists. It was one of the buggy functions used in the first Internet Worm of 1988 (Google for 'morris internet worm'). It is irredeemable; it cannot be used safely in a hostile environment, and all programming has to be done assuming a hostile environment.

To read a line, use fgets().

#include <stdio.h>
#include <string.h>

char global[1000];

int main(void)
{
    printf("Please Enter Text: ");
    if (fgets(global, sizeof(global), stdin) != NULL)
    {
        size_t len = strlen(global);
        if (len != 0 && global[len-1] == '\n')
            global[--len] = '\0';
        printf("%s\n", global);
    }
    return 0;
}

This gets a line of data into global.

You can legitimately ask how len could ever be zero (I asked it of myself, and I replaced assert(len != 0) because of the answer). One answer would be 'standard input was redirected from a binary file and the first byte was a null (zero) byte'. Then fgets() would read data including the null byte up to the first newline, but the strlen() would stop at the null byte, reporting 0 as the length.

The code removes the newline from the string, and determines its length at the same time — you normally need that length. It then prints it. Notice that the code checks that fgets() succeeded. I/O (especially input) has a habit of breaking when you aren't looking. A lot of the time, it will work fine, but to make your program robust, you have to be paranoid about input operations failing (and, later, memory allocations failing).

Upvotes: 3

Rahul Tripathi
Rahul Tripathi

Reputation: 172418

Are you looking for something like this:-

 scanf("%[^\t\n]",&global);

Also in your printf & is not required. It should be like:

printf("%s", global);

Upvotes: 1

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