Ошибка iostream h no such file or directory

Why when I wan to compile the following multi thread merge sorting C program, I receive this error:

ap@sharifvm:~/forTHE04a$ gcc -g -Wall -o mer mer.c -lpthread
mer.c:4:20: fatal error: iostream: No such file or directory
 #include <iostream>
                    ^
compilation terminated.
ap@sharifvm:~/forTHE04a$ gcc -g -Wall -o mer mer.c -lpthread
mer.c:4:22: fatal error: iostream.h: No such file or directory
 #include <iostream.h>
                      ^
compilation terminated.

My program:

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <iostream>
using namespace std;

#define N 2  /* # of thread */

int a[] = {10, 9, 8, 7, 6, 5, 4, 3, 2, 1};  /* target array */

/* structure for array index
 * used to keep low/high end of sub arrays
 */
typedef struct Arr {
    int low;
    int high;
} ArrayIndex;

void merge(int low, int high)
{
        int mid = (low+high)/2;
        int left = low;
        int right = mid+1;

        int b[high-low+1];
        int i, cur = 0;

        while(left <= mid && right <= high) {
                if (a[left] > a[right])
                        b[cur++] = a[right++];
                else
                        b[cur++] = a[right++];
        }

        while(left <= mid) b[cur++] = a[left++];
        while(right <= high) b[cur++] = a[left++];
        for (i = 0; i < (high-low+1) ; i++) a[low+i] = b[i];
}

void * mergesort(void *a)
{
        ArrayIndex *pa = (ArrayIndex *)a;
        int mid = (pa->low + pa->high)/2;

        ArrayIndex aIndex[N];
        pthread_t thread[N];

        aIndex[0].low = pa->low;
        aIndex[0].high = mid;

        aIndex[1].low = mid+1;
        aIndex[1].high = pa->high;

        if (pa->low >= pa->high) return 0;

        int i;
        for(i = 0; i < N; i++) pthread_create(&thread[i], NULL, mergesort, &aIndex[i]);
        for(i = 0; i < N; i++) pthread_join(thread[i], NULL);

        merge(pa->low, pa->high);

        //pthread_exit(NULL);
        return 0;
}

int main()
{
        ArrayIndex ai;
        ai.low = 0;
        ai.high = sizeof(a)/sizeof(a[0])-1;
        pthread_t thread;

        pthread_create(&thread, NULL, mergesort, &ai);
        pthread_join(thread, NULL);

        int i;
        for (i = 0; i < 10; i++) printf ("%d ", a[i]);
        cout << endl;

        return 0;
}

Why when I wan to compile the following multi thread merge sorting C program, I receive this error:

ap@sharifvm:~/forTHE04a$ gcc -g -Wall -o mer mer.c -lpthread
mer.c:4:20: fatal error: iostream: No such file or directory
 #include <iostream>
                    ^
compilation terminated.
ap@sharifvm:~/forTHE04a$ gcc -g -Wall -o mer mer.c -lpthread
mer.c:4:22: fatal error: iostream.h: No such file or directory
 #include <iostream.h>
                      ^
compilation terminated.

My program:

#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
#include <iostream>
using namespace std;

#define N 2  /* # of thread */

int a[] = {10, 9, 8, 7, 6, 5, 4, 3, 2, 1};  /* target array */

/* structure for array index
 * used to keep low/high end of sub arrays
 */
typedef struct Arr {
    int low;
    int high;
} ArrayIndex;

void merge(int low, int high)
{
        int mid = (low+high)/2;
        int left = low;
        int right = mid+1;

        int b[high-low+1];
        int i, cur = 0;

        while(left <= mid && right <= high) {
                if (a[left] > a[right])
                        b[cur++] = a[right++];
                else
                        b[cur++] = a[right++];
        }

        while(left <= mid) b[cur++] = a[left++];
        while(right <= high) b[cur++] = a[left++];
        for (i = 0; i < (high-low+1) ; i++) a[low+i] = b[i];
}

void * mergesort(void *a)
{
        ArrayIndex *pa = (ArrayIndex *)a;
        int mid = (pa->low + pa->high)/2;

        ArrayIndex aIndex[N];
        pthread_t thread[N];

        aIndex[0].low = pa->low;
        aIndex[0].high = mid;

        aIndex[1].low = mid+1;
        aIndex[1].high = pa->high;

        if (pa->low >= pa->high) return 0;

        int i;
        for(i = 0; i < N; i++) pthread_create(&thread[i], NULL, mergesort, &aIndex[i]);
        for(i = 0; i < N; i++) pthread_join(thread[i], NULL);

        merge(pa->low, pa->high);

        //pthread_exit(NULL);
        return 0;
}

int main()
{
        ArrayIndex ai;
        ai.low = 0;
        ai.high = sizeof(a)/sizeof(a[0])-1;
        pthread_t thread;

        pthread_create(&thread, NULL, mergesort, &ai);
        pthread_join(thread, NULL);

        int i;
        for (i = 0; i < 10; i++) printf ("%d ", a[i]);
        cout << endl;

        return 0;
}

You should change iostream.h to iostream. I was also getting the same error as you are getting, but when I changed iostream.h to just iostream, it worked properly. Maybe it would work for you as well.

In other words, change the line that says:

#include <iostream.h>

Make it say this instead:

#include <iostream>

The C++ standard library header files, as defined in the standard, do not have .h extensions.

As mentioned Riccardo Murri’s answer, you will also need to call cout by its fully qualified name std::cout, or have one of these two lines (preferably below your #include directives but above your other code):

using namespace std;

using std::cout;

The second way is considered preferable, especially for serious programming projects, since it only affects std::cout, rather than bringing in all the names in the std namespace (some of which might potentially interfere with names used in your program).