Add simple Makefile

Add get_nproc func

Author: zielinsky

.gitignore

@@ -2,3 +2,5 @@ a.out
 .vscode/c_cpp_properties.json
 .vscode/launch.json
 .vscode/settings.json
+reader
+reader.o

Makefile

@@ -0,0 +1,12 @@
+CC = gcc -g
+CFLAGS = -O3 -Wall -Werror
+
+OBJS = reader.o
+
+reader: $(OBJS)
+	$(CC) $(CFLAGS) -o reader $(OBJS)
+
+reader.o: reader.c reader.h
+
+format:
+	clang-format --style=file -i *.c *.h

reader.c

@@ -1,40 +1,53 @@
+#include "reader.h"
 #include <stdio.h>
-#include <string.h>
 #include <stdlib.h>
-#include "reader.h"
+#include <string.h>
+
+int get_nproc() {
+  FILE *fp;
+  char output[64];
+
+  fp = popen("nproc", "r");
+  if (fp == NULL) {
+    printf("Reading number of threads failed\n");
+    exit(1);
+  }
+
+  int nproc = 0;
+  if (fgets(output, sizeof(output) - 1, fp) != NULL) {
+    sscanf(output, "%d", &nproc);
+  }
+
+  pclose(fp);
+  return nproc;
+}
 
 int main() {
-    FILE* file = fopen("/proc/stat", "r");
-    char line[1024];
-    struct proc_stat* stats = NULL;
-    int thread_count = 0;
-    int capacity = 0;
-
-    while (fgets(line, sizeof(line), file)) {
-        if (strncmp(line, "cpu", 3) == 0) {
-            if (thread_count == capacity) {
-                capacity = capacity == 0 ? 1 : capacity * 2;
-                struct proc_stat* temp = realloc(stats, capacity * sizeof(struct proc_stat));
-                if(temp == NULL) {
-                    perror("Error reallocating memory");
-                    free(stats);
-                    fclose(file);
-                    return 1;
-                }
-                stats = temp;
-            }
-            sscanf(line, "%s %lu %lu %lu %lu %lu %lu %lu %lu %lu %lu", stats[thread_count].name, &stats[thread_count].user, &stats[thread_count].nice, &stats[thread_count].system, &stats[thread_count].idle, &stats[thread_count].iowait, &stats[thread_count].irq, &stats[thread_count].softirq, &stats[thread_count].steal, &stats[thread_count].guest, &stats[thread_count].guest_nice);
-            thread_count++;
-        }else{
-            break;
-        }
-    }
+  FILE *file = fopen("/proc/stat", "r");
+  char line[1024];
+  struct proc_stat stats[get_nproc() + 1];
+  int thread_count = 0;
 
-    for (int i = 0; i < thread_count; i++) {
-        printf("%s %lu %lu %lu %lu %lu %lu %lu %lu %lu\n", stats[i].name, stats[i].user, stats[i].nice, stats[i].system, stats[i].idle, stats[i].iowait, stats[i].irq, stats[i].softirq, stats[i].steal, stats[i].guest, stats[i].guest_nice);
+  while (fgets(line, sizeof(line), file)) {
+    if (strncmp(line, "cpu", 3) == 0) {
+      sscanf(line, "%s %lu %lu %lu %lu %lu %lu %lu %lu %lu %lu",
+             stats[thread_count].name, &stats[thread_count].user,
+             &stats[thread_count].nice, &stats[thread_count].system,
+             &stats[thread_count].idle, &stats[thread_count].iowait,
+             &stats[thread_count].irq, &stats[thread_count].softirq,
+             &stats[thread_count].steal, &stats[thread_count].guest,
+             &stats[thread_count].guest_nice);
+      thread_count++;
     }
+  }
+
+  for (int i = 0; i < thread_count; i++) {
+    printf("%s %lu %lu %lu %lu %lu %lu %lu %lu %lu %lu\n", stats[i].name,
+           stats[i].user, stats[i].nice, stats[i].system, stats[i].idle,
+           stats[i].iowait, stats[i].irq, stats[i].softirq, stats[i].steal,
+           stats[i].guest, stats[i].guest_nice);
+  }
 
-    free(stats);
-    fclose(file);
-    return 0;
+  fclose(file);
+  return 0;
 }

reader.h

@@ -1,5 +1,17 @@
-
 struct proc_stat {
-    char name[256];
-    unsigned long user, nice, system, idle, iowait, irq, softirq, steal, guest, guest_nice;
+  char name[256];
+  unsigned long user, // Time spent with normal processing in user mode.
+      nice,           // Time spent with niced processes in user mode.
+      system,         // Time spent running in kernel mode.
+      idle,           // Time spent in vacations twiddling thumbs.
+      iowait,     // Time spent waiting for I/O to completed. This is considered
+                  // idle time too.
+      irq,        // Time spent serving hardware interrupts.
+      softirq,    // Time spent serving software interrupts.
+      steal,      // Time stolen by other operating systems running in a virtual
+                  // environment.
+      guest,      // Time spent for running a virtual CPU or guest OS under the
+                  // control of the kernel.
+      guest_nice; // Time spent running a niced guest (virtual CPU for guest
+                  // operating systems under the control of the Linux kernel).
 };