Returning Array of pointers to string - c

I am confused and clueless as how can I return an Array of pointers to a String(Basically 2D array) from a function.
What I did(or about to do )in this code is , first insert words/names and then stored it in the array and also input the number 'n'. Than I passed this array and number into the function and their extracted the last 'n' names/words from the array and print that in the main.
Here is my code :
#include<stdio.h>
#include<conio.h>
#include<alloc.h>
#include<string.h>
char** fun(char *s[5],int no)
{
char *f[5];
int i,j=0;
for(i=5-no;i<5;i++)
{
f[j]=(char*)malloc(strlen(s[i])+1);
strcpy(f[j],s[i]);
j++;
}
/*for(j=0;j<no;j++) //I did it just to check whether 'f' stores the last 'n' names.
printf("\n%d. %s",j+1,f[j]);*/
return f;
}
void main()
{
char *name[5],*str,*list[5];
int i,n;
clrscr();
printf("Enther the Names of the list : " );
for(i=0;i<5;i++)
{
printf("%d. ",i+1);
str=(char*)malloc(30);
gets(str);
name[i]=(char*)malloc(strlen(str)+1);
strcpy(name[i],str);
free(str);
}
clrscr();
printf("\nEntered Names are : ");
for(i=0;i<5;i++)
printf("\n%d. %s",i+1,name[i]);
printf("\n Enter the no. :");
scanf("%d",&n);
*list=*fun(name,n); // I am little confused as to how should I wrote this ?
for(i=0;i<n;i++)
printf("\n%d. %s",i+1,list[i]);
getch();
}
Suppose I gave the Input as :
1.the
2.there
3.this
4.that
5.therefore
Enter the No.: 3
Output:
1.this
2.<Some special characters>
3.<Some special characters>
I would more interested in the method which uses the pointer approach .
PS: I am Using Turbo C/C++ IDE as I am in a Learning phase of C .

As H2CO3 pointed out, define the fun as fun(list, name, n); where list is your output list of string. Pass the list from main(), fill it up inside fun().

You can not define array of pointers of char locally(which will allocate it on stack. scope of it is inside that function only) and use it globally.
inside fun() you can use
char f = (char)malloc(sizeof(char*[5])); (allocate memory on heap which you can use it globally)
instead of
char *f[5];
code should be:
#include<stdio.h>
#include<conio.h>
#include<string.h>
#include <malloc.h>
char** fun(char *s[5],int no)
{
char **f = (char**)malloc(sizeof(char*[5]));
int i,j=0;
for(i=5-no;i<5;i++)
{
f[j]=(char*)malloc(strlen(s[i])+1);
strcpy(f[j],s[i]);
j++;
}
/*for(j=0;j<no;j++) //I did it just to check whether 'f' stores the last 'n' names.
printf("\n%d. %s",j+1,f[j]);*/
return f;
}
void main()
{
char *name[5],*str,**list;
int i,n;
printf("Enther the Names of the list : " );
for(i=0;i<5;i++)
{
printf("%d. ",i+1);
str=(char*)malloc(30);
gets(str);
name[i]=(char*)malloc(strlen(str)+1);
strcpy(name[i],str);
free(str);
}
printf("\nEntered Names are : ");
for(i=0;i<5;i++)
printf("\n%d. %s",i+1,name[i]);
printf("\n Enter the no. :");
scanf("%d",&n);
list=fun(name,n); // I am little confused as to how should I wrote this ?
for(i=0;i<n;i++)
printf("\n%d. %s",i+1,list[i]);
getch();
}

Related

program returning garbage values even after declaring variables in c

how do i correct this
i didn't use structure intentionally
this is a program to input student's name, subject and marks.
in the last block, the array (subject+f) 's 1st subscript is returning garbage values while the rest subscript are returning desired result.
i have also posted the image of output as link.
#include<stdio.h>
#include<string.h>
int main()
{
int size,i,k,sub,a=0,reference;
int temp,sorted;
char temp_s[10];
char temp_sb[10];
printf("enter the size of class\n");
scanf("%d",&size);
printf("how many subjects are there?\n");
scanf("%d",&sub);
reference = sub;
char name[size][20];
char subject[size*sub][20];
int marks[sub*size];
int total,subtotal,retotal;
for(k=0;k<sub;k++)
{
printf("so what's the no. %d subject\n",k+1);
scanf(" %s",(subject[k]));
}
for(i=0;i<size;i++)
{
int j,k=0;
printf("Enter a name of student %d\n",i+1);
scanf(" %s",(name+i));
for(j=a;j<reference;j++)
{
printf("enter marks of %s\n",(subject[k]));
scanf("%d",(marks+j));
k++;
}
a=j;
reference=sub+j;
}
reference=sub;
a=0;
printf("\n list of students and marks:\n");
for(i=0;i<size;i++)
{
int j,f=0;
printf("%s\n",(name+i));
for(j=a;j<reference;j++)
{
printf("%s %d\n",(subject[f]),(marks[j]));
f++;
}
a=j;
reference=sub+j;
}
}
Besides the problem with length of names and subjects, this here is a major problem:
(subject+k)
You are probably misunderstanding the subject[k] and *(subject + k) equivalent.
The variable subject is an array of arrays. That means subject[i] is an array (of char and can be used as a zero-terminated string).
The expression (subject + k) is a pointer to the array in subject[k]. It's equal to &subject[k] which have the type char (*)[10]. It's can not be used as a zero-terminated string without dereferencing. So either use *(subject + k) or the simple, less-to-write and easier-to-read subject[k].
I think you also need to change
int marks[sub];
to
int marks[size * sub];
one mark for each subject for each student, correct?

(C) Print an array of structs from a function that calls other function

I cooked a code for a program that asks the user to fill in information about a person (ReadDate/ReadPerson), then it asks for the range of people the user wants to print, and the function prints these people. (PrintRange)
I don't understand why the program is not working; it's stuck on the point when it should print the person... it's means there is probably a problem in either PrintPerson or PrintDate, or in the way I am calling these functions.
Here is my code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct{
int day, month, year;
} Date;
typedef struct{
char *first_name, *last_name;
int id;
Date birthday;
} Person;
void ReadDate(Date *a)
{
printf("Enter the day: ");
scanf("%d", &a->day);
printf("Enter the month (1-12): ");
scanf("%d", &a->month);
printf("Enter the year: ");
scanf("%d", &a->year);
}
void ReadPerson(Person *b)
{
char temp_first_name[21];
char temp_last_name[21];
printf("Enter the first name: ");
gets(temp_first_name);
b->first_name = (char*)malloc(strlen(temp_first_name)+1);
strcpy(b->first_name,temp_first_name);
//need to check malloc (later)
printf("Enter the last name: ");
gets(temp_last_name);
b->last_name = (char*)malloc(strlen(temp_last_name)+1);
strcpy(b->last_name, temp_last_name);
//need to check malloc (later)
printf("Enter the id number: ");
scanf("%d",&b->id);
printf("Enter the birthday:\n");
ReadDate(&b->birthday);
}
int ReadAllDate (Person *b)
{
//Person* b;
int count=1;
char choice;
printf("Would you like to enter a person?(y,n)\n");
choice = getchar();
while(choice == 'y')
{
b = (Person*)malloc(1 * sizeof(Person));
getchar();
ReadPerson(b);
printf("Done!\n");
count++;
getchar();
printf("Would you like to add a person?(y,n)\n");
choice = getchar();
}
count--;
printf("The number of entered persons is %d\nBye\n", count);
return count;
}
void PrintPerson(Person b)
{
printf("%s %s %d\n", b.first_name, b.last_name, b.id);
}
void PrintDate(Date a)
{
printf("%d // %d // %d\n",a.day,a.month,a.year);
}
void PrintRange(Person *b,int count,int ind1,int ind2)
{
int i;
if (ind1<0 || ind1>ind2 || ind2>count)
{
printf("error! you slip out from the limits of the array.\n");
}
else
{
for (i=ind1; i<=ind2; i++)
{
PrintPerson(*(b+i));
PrintDate((b+i)->birthday);
}
}
}
int main(int argc, const char * argv[])
{
Person* b;
int count;
int ind1, ind2;
count = ReadAllDate(b);
printf("insert the first index (the smaller): ");
scanf("%d", &ind1);
printf("insert the second index (the bigger): ");
scanf("%d", &ind2);
PrintRange(b, count, ind1, ind2);
}
The problem is that nowhere you are actually creating an array of Person objects. The function ReadAllDate() never changes the value of the variable b in main(). Instead, for every person you read in, it allocates memory for it, and stores the pointer to that Person in the local variable b in ReadAllDate(). Every time it does it, it forgets the previous value of b.
In main(), the value of b is unitinialized all the time. When you are trying to print persons, it will most likely crash or print garbage.
I see other issues with your code:
Don't use gets(), always use fgets(). The former can write past the end of the buffer you are providing.
Don't do malloc(strlen(...))+strcpy(), use strdup().
Start with count = 0, that way you don't need the count-- in ReadAllDate(). As a computer programmer, it's best to count from zero instead of one.
Write b[i] instead of *(b+i), and b[i].birthday instead of (b+i)->birthday.

Simple print string array

Please let me know what is the mistake with this simple code.
#include<stdio.h>
#include<conio.h>
void main()
{
int i,n;
char a[100];
clrscr();
printf("\n Enter the size of the array");
scanf("%d",&n);
printf("\n Enter the array");
for(i=0;i<n;i++)
scanf("%s",a[i]);
printf("\n Your array is \n");
for(i=0;i<n;i++)
printf("%s",a[i]);
getch();
}
My input is
Enter the size of the array
2
Enter the array
Apple
Banana
Your array
(null) (null)
Can someone explain why this is? Where am i going wrong?
Even if my input is single characters like a or s, this is the same output.
Thanks in advance
You are not declaring array of string itself.
By char a[100]; means you are declaring an array which can hold 100 characters (one of them should be NULL for proper string termination). In other words you are declaring only one string.
Whereas you want an array of strings, thus you need to do something like char a[10][100];. This will declare an array of 10 strings, where every string can hold 100 characters.
After updating your code with char a[10][100];, I am getting following o/p (which you are looking for):
Enter the size of the array3
Enter the arrayhi
hello
com
Your array is
hi
hello
com
There are a few problems here.
When calling scanf, you need to use the & operator and pass the address of the string, e.g.
scanf("%s", &a[i]);
Next is that a is an array of char, not an array of strings. You might try
char a[20][100];
giving you 100 strings of 20 chars.
I edit your code check:
#include<stdio.h>
void main()
{
int i,n;
char a[100];
printf("\n Enter the size of the array: \n");
scanf("%d",&n);
for(i=0;i<n;i++){
printf("\n Enter the array value: \n");
int input;
scanf("%d",&input);
a[i] = input;
}
printf("\n Your array is : ");
for(i=0; i<n; i++)
printf("%d , ",a[i]);
printf("\n");
}
your mistake was in the time to read the value and assign it to the array

String manipulation in C?

Okay I am trying to ask and sort names in C. I completed the code and it compiled without an error but I have a problem. When I input mixed characters that is Uppercase and Lowercase I get Uppercase sorted first and not in order. What should I do to my code ? Please anyone help me.
Code:
#include <stdio.h>
#include <string.h>
int main()
{
char name[30][25],temp[25];
int i,j,n;
printf("Enter how many students : ");
scanf("%d",&n);
for(i=0;i<n;i++);
{
printf("Enter the name of the student : ");
scanf("%s",name[i]);
}
for(i=0;i<n;i++)
{
for(j=i+1;j<n;j++)
{
if(strcmp(name[i],name[j])>0)
{
strcpy(temp,name[i]);
strcpy(name[i],name[j]);
strcpy(name[j],temp);
}
}
}
printf("The sorted names are : \n");
for(i=0;i<n;i++)
{
printf("%s\n",name[i]);
}
getch();
return(0);
}
The loops for your bubble sort are wrong - change:
for(i=0;i<n;i++)
{
for(j=i+j;j<n;j++)
{
to:
for(i=0;i<n-1;i++)
{
for(j=i+1;j<n;j++)
{
Alternatively just use qsort from the standard C library rather than trying to re-invent the wheel.
You have two options. One, convert the string to lower (or upper) before comparison. Secondly strcol each string, this puts k next to K etc. Both methods are destructive so you may need to create a work string and free it after comparison.
First of all your program is wrong. For example instead of
scanf("%s",&name[i]);
there has to be
scanf("%s", name[i]);
Or in this statement
for(j=i+j;j<n;j++)
there is used uninitialized variable j.
As for your question then you should convert strings to upper case using standard C function toupper declared in header <ctype.h>
Also it is better to use selection sort without copying strings every time when name[j] is less than name[i].
Multiple errors:
do not end the for loop with a semicolon
for(i=0;i<n;i++);
take a second look at these variables
for(i=0;i<n;i++)
{
for(j=i+1;j<n;j++)
{
as you described you compare incorrectly for your usecase
if(strcmp(name[i],name[j])>0)
This is a possible solution:
#include <stdio.h>
#include <string.h>
char * Inputs[] =
{
"3\n",
"Carl\n",
"Frank\n",
"carl\n"
};
int in = 0;
int main()
{
char name[30][25],temp[25];
int i,j,n;
printf("Enter how many students : \n");
sscanf(Inputs[in++],"%i",&n);
printf("You entered : %i\n", n);
for(i=0;i<n;i++)
{
printf("Enter the name of the student : \n");
sscanf(Inputs[in++],"%s",&name[i]);
printf("You entered : %s\n", name[i]);
}
for(i=0;i<n-1;i++)
{
for(j=i+1;j<n;j++)
{
if(stricmp(name[i],name[j])>0)
{
strcpy(temp,name[i]);
strcpy(name[i],name[j]);
strcpy(name[j],temp);
}
}
}
printf("The sorted names are : \n");
for(i=0;i<n;i++)
{
printf("%s\n",name[i]);
}
getch();
return(0);
}

Two Dimensional Array of Characters in C

Help me to get out of this problem. I'm using GCC on ubuntu12.04. While I write this program to get 5 strings from keyboard n then print these strings on screen. Program is compiled but during execution it takes strings from keyboard but print only last string. The program which I have written is below:
void main()
{
char names[10];
int i,j;
for(i=0;i<5;i++)
{
printf(" Enter a name which you want to register\n");
scanf("%s",names);
}
for(i=0;i<5;i++)
printf(" the names you enter are %s\n", names);
}
1) you can use 2D char array in this way
char names[5][100];
each line in the 2D array is an array of char with size = 100
for(i=0;i<5;i++)
{
printf(" Enter a name which you want to register\n");
scanf("%99s",names[i]);
}
2) You can use array of pointers in this way
char *names[5];
each element in the array is a pointer to a string (char array). you have to assign each pointer in the array to a memory space before you call scanf()
for(i=0;i<5;i++)
{
names[i]=malloc(100);
printf(" Enter a name which you want to register\n");
scanf("%99s",names[i]);
}
3) if you compile with gcc version >2.7 then your scanf() can allocate memory by using "%ms" instead of "%s"
char *names[5];
for(i=0;i<5;i++)
{
printf(" Enter a name which you want to register\n");
scanf("%ms",&names[i]);
}
There is a simple example about reading and keeping string in the char array.
#include <stdio.h>
const int MACRO = 6;
int main() {
printf("Hello Admin Please Enter the Items:\n");
char items[MACRO][20];
for (int i = 0; i < MACRO; ++i) {
scanf("%19s", items[i]);
}
for (int i = 0; i < MACRO; ++i) {
printf("%s ", items[i]);
}
return 0;
}
In your program the mistake is that you have not putted '&'address of operator int the first for loop . names in your case is an array if you store %s string in names and not &names[0] or &names[1] or so on then as array itself acts as a pointer therefore the array "names" is pointing to the address of its first elements i.e. names[0] . so if you are writing scanf("%s",names); that is similar to scanf("%s",&names[0]); so as you are storing the names in one element only and that too for 5 iterations for only the last string you have entered will be stored and previous strings will be gone . so onlye last string is printed in your program .
in your code, you only declare char data type to be one dimensional and thus it will always overwrite the previous input,that's why the result is the last input printed 5 times.
char names[10];
the above declaration means that you declare a char type variable only with 10 character size without an extra array,it means you only declare a single variable for 5 input.
to make a two dimensional char, you will need to declare it like this :
char names[5][10];
in the code above, it means that you declare a char type variable with 10 character size in an array of 5.
Here is the code I wrote using pointer.
#include <stdio.h>
void main()
{
char *string[100];
int ln;
printf("Enter numbar of lines: ");
scanf("%d",&ln);
printf("\n");
for(int x=0;x<ln;x++)
{
printf("Enter line no - %d ",(x+1));
scanf("%ms",&string[x]); // I am using gcc to compile file, that's why using %ms to allocate memory.
}
printf("\n\n");
for(int x=0;x<ln;x++)
{
printf("Line No %d - %s \n",(x+1),string[x]);
}
}
Another code using two dimensional Array
#include <stdio.h>
void main()
{
int ln;
printf("Enter numbar of lines: ");
scanf("%d",&ln);
printf("\n");
char string[ln][10];
for(int x=0;x<ln;x++){
printf("Enter line no - %d ",(x+1));
scanf("%s",&string[x][0]);
}
for(int x=0;x<ln;x++)
{
printf("Line No %d - %s \n",(x+1),string[x]);
}
}

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