Accessing Global Const Char Pointer Arrays in C/C++

In C/C++, to access a global const char pointer array defined in a header file from another file, you can follow these steps:

1. Define the array in a header file (common.h) using extern keyword to declare it as external:

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// common.h
extern const char *lookup_str[];

2. Define the array in a source file (common.c) without the extern keyword:

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// common.c
#include "common.h"

const char *lookup_str[] = {"test Str0", "test Str1", "test Str2", "test Str3"};

3. Include the header file in the files where you want to use the array and access it:

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// file1.c
#include "common.h"
#include 

int main() {
    int ret = 3;
    std::string r = lookup_str[ret];
    return 0;
}

This way, you can use the lookup_str array in all your C files by including the common.h header file. Note that in C++, you should include for using std::string.

Also, make sure that common.c is compiled and linked with other files that use lookup_str.

When working with global const char pointer arrays in C/C++, there are a few things to keep in mind:

1. Initialization: Global variables can be initialized only once. In your case, the initialization extern const char *lookup_str[] = {"test Str0", "test Str1", "test Str2", "test Str3"}; should be done in a source file (e.g., common.c), not in the header file (common.h). In the header file, declare the array using extern.

2. Include Guards: Use include guards in your header file to prevent multiple inclusion. For example:

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   // common.h
   #ifndef COMMON_H
   #define COMMON_H
   
   extern const char *lookup_str[];
   
   #endif /* COMMON_H */
   

3. Accessing the Array: To access the array from another file, include the common.h header file at the beginning of the file where you want to use the array:

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   #include "common.h"
   

4. File Structure: Make sure your project structure and build system are set up correctly to compile and link all source files together. For example, if you’re using a makefile, ensure that all source files are listed for compilation and linking.

5. C++ String: Since you’re using C++, consider using std::string for string manipulation instead of C-style strings. If you’re working in C++, you should include for std::string usage.

Following these guidelines should help you correctly access and use the global const char pointer array in your C/C++ project.