String allocation to string pointer

[devbegin]

Team,

I am trying to read the string from user and the allocate it to the another string which is ptr string but not successful, so not sure what am I missing here.

Do I have to use any dynamic memory allocation here?

int main(){

    char test[5];
    char *strng, *base;
    int i;

    base=strng;
    for(i=0; i<4; i++){

printf("Enter the value of element %d: ",i);
        scanf("%s",test);
        strng=test;   <<<<<< is this valid?
        strng++; <<< want to store value of test to strng and then move strng to next block so I can store new value.

    }
    
//Following is to print the value that I stored from test to strng.
    strng= base;
    for(i=0; i<4; i++){
printf("value of strng is %s\n", strng);
        strng++;
    }


}

It will be great if you can point me to any reference or doc to read about it.

[stahta01]

Read the link on Pointers Pointers in C - Tutorial - Cprogramming.com

You are missing what a pointer is in C; what you are doing is NOT correct or safe to do.

I have decided that Pointers are beyond my ability to explain it to anyone.

Tim S.

[devbegin]

So what will be corrected code snip?

[DeadPlanet]

It's hard to tell what you're trying to do.

If you want to keep all the user input separate then you probably want an array of arrays. char arr2d[4][5]; is a 2d array with 4 rows and 5 columns (essentially).

If you want to concatenate user input then you can just allocate one string. char strng[20]; is an array of 20 characters. You can then copy each input into the end of whatever you have in the array.

Also you cannot use = to copy strings (unless you know what you're doing). Use strcpy or preferably strncpy.

You should also try not to use magic numbers and your code is vulnerable to buffer overflow and whatnot but it's probably more important that you properly learn arrays and pointers right now.

[devbegin]

Hi DeadPlanet,

Actually I am trying to read the name in string array test and then trying to copy the same elements in character array strng but its not working. As strng is pointer so I should be able to do strng = test in each iteration of first for loop. However I am not able to achieve it. I want to initialize the strng using pointer so I dont have to worry about how many elements and space. Is malloc is the way to go with strng[i][j]? where i will be number of row of string and j will be base of specific row string array's first char?

[tabstop]

character array strng but its not working. As strng is pointer

This is self-contradictory. Either strng is a character array or a pointer, but not both. If you want a copy, then using a pointer for strng is incorrect, as that wouldn't give you a copy (it would merely give you another name for the same string in memory).

You also seem to think you have more than one string, but you do not. You have one string that can hold up to four characters.

so I dont have to worry about how many elements and space

This is not an option in C. It is your job as the programmer to allocate the memory you need for storage.

[devbegin]

HI Tabstop,

so basically I will have to do sizeof or strlen to find size of it and allocate the space for strng using malloc, that will store one of the string, how about the second string I have, I will have to do same malloc action and assign second string to it, but how will I keep track of the from where first string is stored in strng and how I navigate to all strings which I want to store in strng.

I want to do something like:
strng[0]=abc
strng[1]=abcd

using malloc I will allocate the space for each string but how will I keep track of where those are store and how can I access them using strng[1]?

should I do something like

strng[0][malloc(sizeof(test))]
strng[1][malloc(sizeof(test))]

[devbegin]

This is what I tried for single string:

int main(){
        char *s1;
        char s2;
        int a;


        struct utmp ut;


        a = sizeof(ut.ut_line);
        printf ("Size of line is %d\n",a);


        s1 = malloc(a);
        s1 = "Test";
        printf ("size of s1 is %d\n", sizeof(s1));
        printf("Value of s1 is %s and size is %d\n", s1, sizeof(s1));
}
[root@ c_prog]# ./a.out 
Size of line is 32
size of s1 is 8
Value of s1 is Test and size is 8
[root@ c_prog]#

I used the sizeof to find the size of ut_line which is 32 but s1 is allocated with only 8?

[devbegin]

int main(){
        char *s1;
        char s2;
        int a;


        struct utmp ut;


        a = sizeof(ut.ut_line);
        printf ("Size of line is %d\n",a);


        s1 = malloc(a);
        s1 = "Test is test, what do you say";
        printf ("size of s1 is %d\n", sizeof(s1));
        printf("Value of s1 is %s and size is %d\n", s1, sizeof(s1));
}

I tried with bigger string but it still writes to it, should it not restrict to 8?

./a.out
Size of line is 32
size of s1 is 8
Value of s1 is Test is test, what do you say and size is 8

Value I gave is "Test is test, what do you say" and it took it whole.