Solution program for exercise 3.2 of APUE 3ed

A program with  the same as UNIX system call dup2(2), realized without fcntl(2)

mydup2.c

@@ -0,0 +1,77 @@
+#include <stdio.h>
+#include <assert.h>
+#include <unistd.h>
+
+#define NMAX  1024
+
+int mydup2(const int fd, const int fd2){
+
+    int tmpfd[NMAX], i;
+    /*check fd2 is an illegal value*/
+    if((fd2 < 3)||(fd2 > sysconf(_SC_OPEN_MAX))){
+        return -1;
+    }
+    /*check fd is opened*/
+    if((tmpfd[0] = dup(fd)) == -1){
+        return -1;
+    }
+    /* special case which fd equals fd2 */
+    if(fd == fd2){
+        return fd2;
+    }
+    /*case which fd > fd2*/
+    else{
+
+        if(tmpfd[0] == fd2){
+            return fd2;
+        }
+        else if(tmpfd[0] < fd2){
+            i = 1;
+            while((tmpfd[i++] = dup(fd)) != -1){
+
+                if(tmpfd[i-1] >= fd2){
+
+                    if(tmpfd[i-1] == fd2){
+                        /*close the opened fds*/
+                        for(i-=2; i>=0; i--){
+                            close(tmpfd[i]);
+                        }
+                        break;
+                    }
+                    else{
+                        close(fd2);
+                        tmpfd[i] = dup(fd);
+                        assert(fd2 == tmpfd[i]);
+                        /*close the opened fds*/
+                        close(tmpfd[i-1]);
+                        for(i-=2; i>=0; i--){
+                            close(tmpfd[i]);
+                        }
+                        break;
+                    }
+                }
+            }
+            return fd2;
+        }
+        else{
+            close(fd2);
+            tmpfd[1] = dup(fd);
+            assert(fd2 == tmpfd[1]);
+            /*close the opened fds*/
+            close(tmpfd[0]);
+            return fd2;
+        }
+    }
+}
+
+int main(){
+    int fd;
+
+    fd = dup2(1, 9);
+    printf("The result by dup2 is %d\n", fd);
+    fd = mydup2(2, 5);
+    printf("The result by mydup2 is %d\n", fd);
+
+    return 0;
+
+}