Why is the generated txt file empty?

Why is the generated txt file empty? The following code does not have any conditions before, but generates an empty file if (! File_exists("shang_ci_zong_shu_1.txt & quot;) {// (value generated for the first time) if the total number of files does not exist, the generated txt file. $ handle = fope why is the generated txt file empty?
The following code does not have any conditions before, but an empty file is generated.

If (! File_exists ("shang_ci_zong_shu_1.txt") {// (value generated for the first time) if the total number of files does not exist, a txt file is generated.
Export handleappsfopen('shang_ci_zong_shu_1.txt ', "w ");
Echo "aa"; // The output is successfully tested, but an empty file is generated.
Fwrite ($ handle, "1"); // generate default value 1
Fclose ($ handle );
}

There is no problem in the if statement test below ..
Export handleappsfopen('shang_ci_zong_shu_1.txt ', "w ");
Fwrite ($ handle, "1"); // generate default value 1
Fclose ($ handle );

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You can determine the return value of fwrite to see what it is.
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You cannot understand. Your file exists. Naturally, it will not enter the if branch.