system可以执行(popen无法执行）

#include <stdio.h>
#include <string.h>
#define BUF_SIZE         1024
#define MAX_NAME_SIZE     1024
int running_command(const char *command,char *result)
{
    FILE *fp = NULL;
    char buffer[BUF_SIZE] = {0};
    if (!command || !(fp = popen(command,"r"))){
        fprintf(stderr,"%s %s %d was error\n",__FILE__,__func__,__LINE__);
        return -1; 
    }   
    fread(buffer,MAX_NAME_SIZE,1,fp);
    strcpy(result,buffer);
    fclose(fp);
    return 0;
}
int main()
{
  char paht[256];
//  running_command("",paht);
  system("ps -aux");
  printf("%s",paht);
  return 0;
}