php session验证码不一致总显示上次验证码的解决方法

    $(".login").live('click',function(){
        var username=$(".input_user").val();
        var password=$(".input_ps").val();
        var code=$('.input_checkcode').val();
        if(username==""){
            alert("用户名不能为空");
            return false;
        }
        if(password==""){
            alert("密码不能为空");
            return false;
        }
        var URL="checkLogin.php?";
        var DATA="&username="+username+"&password="+password+"&code="+code;
        $.getJSON(URL+DATA,function(json){
            if(json.code=='code_error'){
                alert('验证码错误，请重新输入验证码');
            }
            if(json.username=='true_u'&&json.password=='true_p'){
                //alert(json.username+"|"+username+'...1');
                window.location="index.php";
            }
            if(json.username=='error_u'||json.password=='error_p'){
                alert("用户名输入或密码输入有误，请检查后重新登陆!");
                window.location="login.php";
            }
        });
    });

后台checkLogin.php关键代码：

$code=$_GET['code'];
            if($code!=$_SESSION['captchaCode']['content'])
                {$adminInfo['code']='code_error';};

            if($row['username']==$username&&$row['password']==$password){

                $_SESSION['username']=$row['username'];
                $adminInfo['username']='true_u';
                $adminInfo['password']='true_p';
                mysql_close();
            }else
            if($row['username']!=$username){
                $adminInfo['username']='error_u';
            }
            if($row['password']!=$password){
                $adminInfo['password']='error_p';
            }

            //var_dump($adminInfo);exit;
            echo json_encode($adminInfo);

具体如下： checkCode.class.php//验证码

/*
* Captcha Class base on PHP GD Lib
* @author Design
* @version 1.0
* @copyright js8.in 2010 bbs.it-home.org
* @demo
* include('captchaClass.php');
* $captchaDemo=new Captcha();
* $captchaDemo->createImage();
*/
class Captcha{
 //@定义验证码图片高度
 private $height;
 //@定义验证码图片宽度
 private $width;
 //@定义验证码字符个数
 private $textNum;
 //@定义验证码字符内容
 private $textContent;
 //@定义字符颜色
 private $fontColor;
 //@定义随机出的文字颜色
 private $randFontColor;
 //@定义字体大小
 private $fontSize;
 //@定义字体
 private $fontFamily;
 //@定义背景颜色
 private $bgColor;
 //@定义随机出的背景颜色
 private $randBgColor;
 //@定义字符语言
 private $textLang;
 //@定义干扰点数量
 private $noisePoint;
 //@定义干扰线数量
 private $noiseLine;
 //@定义是否扭曲
 private $distortion;
 //@定义扭曲图片源
 private $distortionImage;
 //@定义是否有边框
 private $showBorder;
 //@定义验证码图片源
 private $image;

 //@Constructor 构造函数
 public function Captcha(){
 $this->textNum=4;
 $this->fontSize=16;
 $this->fontFamily='c:\\windows\\fonts\SIMYOU.ttf';//设置中文字体，可以改成linux的目录
 $this->textLang='en';
 $this->noisePoint=30;
 $this->noiseLine=3;
 $this->distortion=false;
 $this->showBorder=false;
 }

 //@设置图片宽度
 public function setWidth($w){
 $this->width=$w;
 }

 //@设置图片高度
 public function setHeight($h){
 $this->height=$h;
 }

 //@设置字符个数
 public function setTextNumber($textN){
 $this->textNum=$textN;
 }

 //@设置字符颜色
 public function setFontColor($fc){
 $this->fontColor=sscanf($fc,'#%2x%2x%2x');
 }

 //@设置字号
 public function setFontSize($n){
 $this->fontSize=$n;
 }

 //@设置字体
 public function setFontFamily($ffUrl){
 $this->fontFamily=$ffUrl;
 }

 //@设置字符语言
 public function setTextLang($lang){
 $this->textLang=$lang;
 }

 //@设置图片背景
 public function setBgColor($bc){
 $this->bgColor=sscanf($bc,'#%2x%2x%2x');
 }

 //@设置干扰点数量
 public function setNoisePoint($n){
 $this->noisePoint=$n;
 }

 //@设置干扰线数量
 public function setNoiseLine($n){
 $this->noiseLine=$n;
 }

 //@设置是否扭曲
 public function setDistortion($b){
 $this->distortion=$b;
 }

 //@设置是否显示边框
 public function setShowBorder($border){
 $this->showBorder=$border;
 }

 //@初始化验证码图片
 public function initImage(){
 if(empty($this->width)){$this->width=floor($this->fontSize*1.3)*$this->textNum+10;}
 if(empty($this->height)){$this->height=$this->fontSize*2;}
 $this->image=imagecreatetruecolor($this->width,$this->height);
 if(empty($this->bgColor)){
 $this->randBgColor=imagecolorallocate($this->image,mt_rand(100,255),mt_rand(100,255),mt_rand(100,255));
 }else{
 $this->randBgColor=imagecolorallocate($this->image,$this->bgColor[0],$this->bgColor[1],$this->bgColor[2]);
 }
 imagefill($this->image,0,0,$this->randBgColor);
 }

 //@产生随机字符
 public function randText($type){
 $string='';
 switch($type){
 case 'en':
 $str='ABCDEFGHJKLMNPQRSTUVWXY3456789';
 for($i=0;$itextNum;$i++){
 $string=$string.','.$str[mt_rand(0,29)];
 }
 break;
 case 'cn':
 for($i=0;$itextNum;$i++) {
 $string=$string.','.chr(rand(0xB0,0xCC)).chr(rand(0xA1,0xBB));
 }
 $string=iconv('GB2312','UTF-8',$string); //转换编码到utf8
 break;
 }
 return substr($string,1);
 }

 //@输出文字到验证码
 public function createText(){
 $textArray=explode(',',$this->randText($this->textLang));
 $this->textContent=join('',$textArray);
 if(empty($this->fontColor)){
 $this->randFontColor=imagecolorallocate($this->image,mt_rand(0,100),mt_rand(0,100),mt_rand(0,100));
 }else{
 $this->randFontColor=imagecolorallocate($this->image,$this->fontColor[0],$this->fontColor[1],$this->fontColor[2]);
 }
 for($i=0;$itextNum;$i++){
 $angle=mt_rand(-1,1)*mt_rand(1,20);
 imagettftext($this->image,$this->fontSize,$angle,5+$i*floor($this->fontSize*1.3),floor($this->height*0.75),$this->randFontColor,$this->fontFamily,$textArray[$i]);
 }
 }

 //@生成干扰点
 public function createNoisePoint(){
 for($i=0;$inoisePoint;$i++){
 $pointColor=imagecolorallocate($this->image,mt_rand(0,255),mt_rand(0,255),mt_rand(0,255));
 imagesetpixel($this->image,mt_rand(0,$this->width),mt_rand(0,$this->height),$pointColor);
 }

 }

 //@产生干扰线
 public function createNoiseLine(){
 for($i=0;$inoiseLine;$i++) {
 $lineColor=imagecolorallocate($this->image,mt_rand(0,255),mt_rand(0,255),20);
 imageline($this->image,0,mt_rand(0,$this->width),$this->width,mt_rand(0,$this->height),$lineColor);
 }
 }

 //@扭曲文字
 public function distortionText(){
 $this->distortionImage=imagecreatetruecolor($this->width,$this->height);
 imagefill($this->distortionImage,0,0,$this->randBgColor);
 for($x=0;$xwidth;$x++){
 for($y=0;$yheight;$y++){
 $rgbColor=imagecolorat($this->image,$x,$y);
 imagesetpixel($this->distortionImage,(int)($x+sin($y/$this->height*2*M_PI-M_PI*0.5)*3),$y,$rgbColor);
 }
 }
 $this->image=$this->distortionImage;
 }

 //@生成验证码图片
 public function createImage(){
 $this->initImage(); //创建基本图片
 $this->createText(); //输出验证码字符
 if($this->distortion){$this->distortionText();} //扭曲文字
 $this->createNoisePoint(); //产生干扰点
 $this->createNoiseLine(); //产生干扰线
 if($this->showBorder){imagerectangle($this->image,0,0,$this->width-1,$this->height-1,$this->randFontColor);} //添加边框
 imagepng($this->image);
 imagedestroy($this->image);
 if($this->distortion){imagedestroy($this->$distortionImage);}
 return $this->textContent;
 }
}
?>
code.php//new 一个对象，负责图片的创建以及验证码文本写入session

session_start();
header("Content-type:image/png");
include('checkCode.class.php');
$captcha5=new Captcha();

//@设置验证码宽度
//$captcha5->setWidth(200);

//@设置验证码高度
//$captcha5->setHeight(50);

//@设置字符个数
$captcha5->setTextNumber(4);

//@设置字符颜色
//$captcha5->setFontColor('#ffffff');

//@设置字号大小
//$captcha5->setFontSize(25);

//@设置字体
$captcha5->setFontFamily('c:\\windows\\fonts\\comic.TTF');

//@设置语言
$captcha5->setTextLang('en');

//@设置背景颜色
//$captcha5->setBgColor('#000000');

//@设置干扰点数量
//$captcha5->setNoisePoint(600);

//@设置干扰线数量
//$captcha5->setNoiseLine(10);

//@设置是否扭曲
//$captcha5->setDistortion(true);

//@设置是否显示边框
$captcha5->setShowBorder(true);

//输出验证码
$code=$captcha5->createImage();
$_SESSION['captchaCode']['content']=$code;
//$_SESSION['captchaCode']['time']=microtime();
?>

login.php//登陆页面，调用生成的验证码图片

  验证码：

复制代码