AgeneratorinPHPisamemory-efficientwaytoiterateoverlargedatasetsbyyieldingvaluesoneatatimeinsteadofreturningthemallatonce.1.Generatorsusetheyieldkeywordtoproducevaluesondemand,reducingmemoryusage.2.Theyareusefulforhandlingbigloops,readinglargefiles,or

To prevent session hijacking in PHP, the following measures need to be taken: 1. Use HTTPS to encrypt the transmission and set session.cookie_secure=1 in php.ini; 2. Set the security cookie attributes, including httponly, secure and samesite; 3. Call session_regenerate_id(true) when the user logs in or permissions change to change to change the SessionID; 4. Limit the Session life cycle, reasonably configure gc_maxlifetime and record the user's activity time; 5. Prohibit exposing the SessionID to the URL, and set session.use_only

You can use substr() or mb_substr() to get the first N characters in PHP. The specific steps are as follows: 1. Use substr($string,0,N) to intercept the first N characters, which is suitable for ASCII characters and is simple and efficient; 2. When processing multi-byte characters (such as Chinese), mb_substr($string,0,N,'UTF-8'), and ensure that mbstring extension is enabled; 3. If the string contains HTML or whitespace characters, you should first use strip_tags() to remove the tags and trim() to clean the spaces, and then intercept them to ensure the results are clean.

In PHP, you can use square brackets or curly braces to obtain string specific index characters, but square brackets are recommended; the index starts from 0, and the access outside the range returns a null value and cannot be assigned a value; mb_substr is required to handle multi-byte characters. For example: $str="hello";echo$str[0]; output h; and Chinese characters such as mb_substr($str,1,1) need to obtain the correct result; in actual applications, the length of the string should be checked before looping, dynamic strings need to be verified for validity, and multilingual projects recommend using multi-byte security functions uniformly.

The urlencode() function is used to encode strings into URL-safe formats, where non-alphanumeric characters (except -, _, and .) are replaced with a percent sign followed by a two-digit hexadecimal number. For example, spaces are converted to signs, exclamation marks are converted to!, and Chinese characters are converted to their UTF-8 encoding form. When using, only the parameter values ??should be encoded, not the entire URL, to avoid damaging the URL structure. For other parts of the URL, such as path segments, the rawurlencode() function should be used, which converts the space to . When processing array parameters, you can use http_build_query() to automatically encode, or manually call urlencode() on each value to ensure safe transfer of data. just

There is no legal virtual currency platform in mainland China. 1. According to the notice issued by the People's Bank of China and other departments, all business activities related to virtual currency in the country are illegal; 2. Users should pay attention to the compliance and reliability of the platform, such as holding a mainstream national regulatory license, having a strong security technology and risk control system, an open and transparent operation history, a clear asset reserve certificate and a good market reputation; 3. The relationship between the user and the platform is between the service provider and the user, and based on the user agreement, it clarifies the rights and obligations of both parties, fee standards, risk warnings, account management and dispute resolution methods; 4. The platform mainly plays the role of a transaction matcher, asset custodian and information service provider, and does not assume investment responsibilities; 5. Be sure to read the user agreement carefully before using the platform to enhance yourself

Bitcoin halving affects the price of currency through four aspects: enhancing scarcity, pushing up production costs, stimulating market psychological expectations and changing supply and demand relationships; 1. Enhanced scarcity: halving reduces the supply of new currency and increases the value of scarcity; 2. Increased production costs: miners' income decreases, and higher coin prices need to maintain operation; 3. Market psychological expectations: Bull market expectations are formed before halving, attracting capital inflows; 4. Change in supply and demand relationship: When demand is stable or growing, supply and demand push up prices.

There are two main ways to get the last N characters of a string in PHP: 1. Use the substr() function to intercept through the negative starting position, which is suitable for single-byte characters; 2. Use the mb_substr() function to support multilingual and UTF-8 encoding to avoid truncating non-English characters; 3. Optionally determine whether the string length is sufficient to handle boundary situations; 4. It is not recommended to use strrev() substr() combination method because it is not safe and inefficient for multi-byte characters.