Why is the output of echo in php not displayed? How to deal with it?

In PHP programming, we often use the echo function to output results. However, sometimes when using echo to output results, we find that the output results are not displayed. This problem troubles many PHP programmers. So, why does this problem occur? In this article, we’ll get to the root of this problem and introduce some possible solutions.

First, let's take a look at Why the echo output is not displayed.

1. Syntax error

Grammar error is a common cause of this problem. PHP syntax is very strict, and a wrong symbol or bracket may cause a program error. Therefore, if your echo statement is spelled incorrectly or if you leave out parentheses, the program will fail. For example, the following echo statement is missing a bracket:

echo "Hello World!;

When executing this statement, the following error message will be prompted:

Parse error: syntax error, unexpected ';', expecting ')' in test.php on line 2

This error tells us that there is a missing ')'.

2. The variable is undefined

If you use an undefined variable in the echo statement, the output result will not be displayed. This problem is compounded if your code uses multiple files that contain variable references. In this case, you need to check that the variable name is spelled correctly and make sure that the variable is defined in the code.

For example, the following echo statement uses undefined variables:

echo $food;

When executing this statement, the following error message will be prompted:

Notice: Undefined variable: food in test.php on line 2

This error tells us $food is an undefined variable.

3. Line break character

Sometimes, the problem that the echo output is not displayed may also be related to the line break character. When you use a newline character in an echo statement, the output may not be displayed.

For example, the following echo statement uses a newline character:

echo "Hello\nWorld";

When this statement is executed, no results may be displayed. So, to avoid this, we can use escape characters in PHP to replace newlines.

For example, we can modify the above code to:

echo "Hello" . PHP_EOL . "World";

In this way, the output results can be displayed normally.

The above are some possible reasons for the problem that echo output is not displayed. So, next we will introduce some solutions.

1. Check for grammatical errors

In PHP programming, grammatical errors are very common errors. Therefore, we need to carefully check whether there are spelling errors, grammatical errors, etc. in the echo statement. question. At the same time, make sure that brackets, quotation marks and other symbols are used correctly. If the program prompts that there is a syntax error, then we need to modify it according to the prompts.

For example, in the following sample code, the echo statement is missing parentheses:

message = "Hello World"; 
echo message;

When the code is executed, the following error message will be prompted:

Parse error: syntax error, unexpected 'message' (T_STRING) in test.php on line 2

This error message We're missing parentheses.

2. Check whether the variable exists

Using undefined variables is also a common reason why the output is not displayed. Therefore, when writing code, we need to ensure that variables are defined. This problem may be more complicated if we use multiple files in a program. In this case we need to check if the variable name is defined in the code and spelled correctly.

For example, in the following example, we try to output an undefined variable $food:

echo $food;

When executing this code, the following error will be prompted:

Notice: Undefined variable: food in test.php on line 2

This error prompts us to define the variable $food.

3. Avoid using newline characters

Using newline characters is also a common reason why the output is not displayed. Therefore, we should try to avoid using them. If we really need to include newlines in the output, we can use escape characters in PHP instead. For example, we can use PHP_EOL to replace newlines.

For example, in the following sample code, we use PHP_EOL to replace the newline character:

echo "Hello" . PHP_EOL . "World";

In this way, the output results can be displayed normally.

Summary

The echo output not being displayed is a relatively common problem, which may be related to syntax errors, undefined variables, newline characters, etc. When encountering this problem, we should first check for syntax errors, make sure the variables have been defined, and try to avoid using newlines. If the problem is not resolved, then we can use debugging tools to track down the source of the problem. When writing code, we should always be alert to avoid these common mistakes.

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