What does the return value of 56 or 65 mean by C language function?

When a C function returns 56 or 65, it indicates a specific event. These numerical meanings are defined by the function developer and may indicate success, file not found, or read errors. Replace these "magic numbers" with enumerations or macro definitions can improve readability and maintainability, such as: READ_SUCCESS, FILE_NOT_FOUND, and READ_ERROR.

C function returns value 56 or 65: those hidden signals

Many beginners may be confused when they see that the C function returns 56 or 65. This is not a magic number, but a "signal light" carefully designed by programmers, conveying information about the execution results of the function. They themselves have no fixed meaning, and they all depend on how the function developers define it. In this article, we will explore the story behind these numbers and how to avoid falling into the trap of "magic numbers".

Background: The conventional "code"

C language does not have rich exception handling mechanisms like some high-level languages. In many cases, the return value of a function is the only feedback channel. Therefore, programmers will agree on some specific values ​​to represent different situations of function execution: success, failure, certain specific error, etc. 56 and 65 are two examples of this conventional "code". They may represent a certain state code or they may be just numbers that programmers choose at will to distinguish different results. The key is that you have to consult the documentation or code comments of the function to understand the true meaning of these numbers.

Peeking into the inner: the perspective of functions

Let's assume a simple example: a function is responsible for reading data from a file. If the read is successful, it may return 0; if the file does not exist, it may return 56; if other errors occur during the read process, it may return 65. It depends entirely on the designer of the function.

 <code class="c">#include <stdio.h> int readFile(const char* filename) { FILE *fp = fopen(filename, "r"); if (fp == NULL) { return 56; // File not found } // ... 读取文件内容... if (/* 读取过程中发生错误*/) { fclose(fp); return 65; // Read error } fclose(fp); return 0; // Success } int main() { int result = readFile("mydata.txt"); if (result == 56) { printf("File not found!\n"); } else if (result == 65) { printf("Read error!\n"); } else { printf("File read successfully!\n"); } return 0; }</stdio.h></code>

In this code, 56 and 65 represent two different error cases. Note that the readFile function does not throw an exception, but instead informs the caller of the execution result of the function by returning the value. This is the typical style of C language, which is simple and direct, but also requires programmers to be more careful.

Traps and warnings: Avoid "magic numbers"

Using numbers like 56 and 65 as status codes directly can easily make the code difficult to understand and maintain. Imagine that in a few months, you or someone else needs to modify this function, and it will be very troublesome if you forget the meaning of these numbers.

A better approach is to use enums or macro definitions instead of these "magic numbers".

 <code class="c">#include <stdio.h> typedef enum { READ_SUCCESS = 0, FILE_NOT_FOUND = 56, READ_ERROR = 65 } ReadResult; ReadResult readFile(const char* filename) { // ... (函数体不变) ... } int main() { ReadResult result = readFile("mydata.txt"); if (result == FILE_NOT_FOUND) { printf("File not found!\n"); } else if (result == READ_ERROR) { printf("Read error!\n"); } else { printf("File read successfully!\n"); } return 0; }</stdio.h></code>

In this way, the readability and maintainability of the code will be greatly improved. Even if the meaning of 56 and 65 is forgotten, FILE_NOT_FOUND and READ_ERROR can clearly express their meanings. This is a good programming habit and is worth learning and reference by all C language programmers.

Experience: Code readability is better than anything else

Remember, the code is written for people to see, and the second is executed for machines. Clear, concise and easy to understand code can not only improve development efficiency, but also reduce maintenance costs and avoid unnecessary errors. Therefore, when writing C language code, be sure to pay attention to the readability of the code, try to avoid using "magic numbers", and use enumerations or macro definitions to improve the comprehensibility of the code. This not only prevents you from falling into a pit, but also makes you a better programmer.

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