PHP 7.1中getData()函数返回值为空但可正常打印，求原因

Hey there, this is a super common gotcha when working with PHP functions—let's break down the most likely reasons your getData() isn't returning content, even though direct print/echo statements work:

1. Your function isn't using return (it's echoing instead) #

This is the #1 culprit. If your getData() function uses echo to output content directly instead of returning it, calling getData() won't pass any value back to the caller. For example:

// Bad: echoes content, doesn't return anything
function getData() {
    echo "Hello from getData!";
}

// This will output nothing (since getData() returns null)
$result = getData();
echo $result;

// But this will output directly (because the function echoes internally)
getData();

If you need to use the function's output elsewhere, replace those echo calls with return statements.

2. Output buffering is swallowing your content #

If getData() uses output buffering functions like ob_start(), you might be discarding the buffered content instead of returning it. PHP 7.1 handles buffering consistently, but a common mistake is:

// Bad: discards buffered content
function getData() {
    ob_start();
    echo "Some content";
    ob_end_clean(); // This throws away the buffer instead of returning it
}

// Fix: return the buffered content
function getData() {
    ob_start();
    echo "Some content";
    return ob_get_clean(); // Returns the buffer and clears it
}

3. Hidden errors are stopping the function #

If getData() hits a fatal error (like calling an undefined function, accessing an undefined variable, or a syntax issue), PHP might silently fail (especially if error reporting is disabled) and return null without any output.

Enable full error reporting temporarily to see what's going on:

error_reporting(E_ALL);
ini_set('display_errors', 1);

This will show you any errors that are crashing the function before it can return a value.

4. The function returns a non-renderable value #

If getData() returns a non-string value (like null, false, or an empty array), echoing it will result in an empty browser output. For example:

function getData() {
    return null; // Or false, or []
}

echo getData(); // Outputs nothing

Use var_dump(getData()); instead of echo to see exactly what the function is returning—this will show you the type and value, even if it's not a printable string.

5. Accidental output before calling getData() #

If there's any whitespace, echo, or print statement before your <?php tag, or before calling getData(), it can send HTTP headers early. In some cases, this can interfere with the function's ability to return content properly (especially if the function tries to set headers later).

Quick Troubleshooting Steps #

• Add var_dump(getData()); right after calling the function to inspect the return value.
• Double-check every line in getData() for return statements.
• Enable error reporting to catch hidden issues.

If you can share a snippet of your getData() code, I can help pinpoint the exact issue!

内容的提问来源于stack exchange，提问作者riten