Abraham Abraham - 4 months ago 43
C Question

Fatal error: iostream: No such file or directory in compiling C program using GCC

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;
}

Seb Seb
Answer

Neither <iostream> nor <iostream.h> are standard C header files. Your code is meant to be C++, where <iostream> is a valid header. Use g++ (and a .cpp file extension) for C++ code.

However, this program uses mostly constructs that are available in C anyway. It's easy enough to convert the entire program to compile using a C compiler. Simply remove #include <iostream> and using namespace std;, and replace cout << endl; with putchar('\n');... I advise compiling using C99 (eg. gcc -std=c99)