Question about the text array for making a Chinese verification code using javascript-php

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When building a php Chinese verification code, the original idea is to split a paragraph into texts to form a text array, traverse four times, and randomly generate four verification texts, it is then painted on the image. However, when 'str _ split ($ str, 3) 'is used to separate the image, sometimes one less text is replaced with 'explode ("", $ str) 'or occasionally missing words... The main code is as follows: '$ fontFace = 'aa. ttf'; $ str = "The Grand gate is the main guide brand of China, and the industry association will re-promote the support and sales of the sponsors "; $ strDb = str_split ($ str, 3); for ($ I = 0; $ I <4; $ I ++) {$ fontColor = imagecolorallocate ($ img, mt_rand (0,120), mt_rand (0,120), mt_rand (0,120); $ index = mt_rand (0, count ($ strDb) + 1 ); $ cn = $ strDb [$ index]; $ captcha. = $ cn; $ x = ($ I * 120/4) + mt_rand (); $ y = mt_rand (); imagettftext ($ img, 15, mt_rand ), $ x, $ y, $ fontColor, $ fontFace, $ cn );} 'I think it is a text encoding problem. When the number of bytes is set to 4, some text can be displayed. But I don't know how to solve it. Please help. Thank you!

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When building a php Chinese verification code, the original idea is to split a paragraph into texts to form a text array, traverse four times, and randomly generate four verification texts, it is then painted on the image. However, when 'str _ split ($ str, 3) 'is used to separate the image, sometimes one less text is replaced with 'explode ("", $ str) 'or occasionally missing words... The main code is as follows: '$ fontFace = 'aa. ttf'; $ str = "The Grand gate is the main guide brand of China, and the industry association will re-promote the support and sales of the sponsors "; $ strDb = str_split ($ str, 3); for ($ I = 0; $ I <4; $ I ++) {$ fontColor = imagecolorallocate ($ img, mt_rand (0,120), mt_rand (0,120), mt_rand (0,120); $ index = mt_rand (0, count ($ strDb) + 1 ); $ cn = $ strDb [$ index]; $ captcha. = $ cn; $ x = ($ I * 120/4) + mt_rand (); $ y = mt_rand (); imagettftext ($ img, 15, mt_rand ), $ x, $ y, $ fontColor, $ fontFace, $ cn );} 'I think it is a text encoding problem. When the number of bytes is set to 4, some text can be displayed. But I don't know how to solve it. Please help. Thank you!

Two vertices. The first is $ str separated by spaces, and the second is-1, not + 1, when a random index is generated.
Index can be used to obtain a random value in an array.array_rand()Function generation
The changes are as follows:

$ FontFace = 'aa. ttf'; $ str = "dashboard is a key recommendation product for Chinese leading brands and industry associations"; $ strDb = str_split ($ str, 3 ); for ($ I = 0; $ I <4; $ I ++) {$ fontColor = imagecolorallocate ($ img, mt_rand (0,120), mt_rand (0,120 ), mt_rand (0,120); $ index = array_rand ($ strDb); $ cn = $ strDb [$ index]; $ captcha. = $ cn; $ x = ($ I * 120/4) + mt_rand (); $ y = mt_rand (); imagettftext ($ img, 15, mt_rand ), $ x, $ y, $ fontColor, $ fontFace, $ cn );}

Use the mb extended function to process strings and solve the encoding problem. What is the space used?

If $ str contains English and Chinese characters, use this delimiter.$strDb=preg_split('//u', $str, -1, PREG_SPLIT_NO_EMPTY);