Can I change a member variable of a struct using a std::map value?

There is a structure that has multiple const char* member variables.

typedef struct WWCryptoAuthorizationHeader
{
    int age;
    const char *name;
    const char *address;
} StudentInfo;

There is a function that takes a (pointer to) this struct and a (C-style) string containing the name of one of the member variables. Within this function, I create a map from member names to their values. Then I find the provided member name in the map. Can I have the function change the designated member of the struct using the value from the map?

I tried the following

void foo(StudentInfo *studentInfo, const char* key)
{
    std::map<std::string, const char*> studentInfoMap;
    
    studentInfoMap.insert(std::make_pair("name", studentInfo->name));
    studentInfoMap.insert(std::make_pair("address", studentInfo->address));

    for(auto &item : studentInfoMap)
    {
       if (strcmp(key, item.first.c_str()) == 0)
       {
          item.second = "John";
       }
    }
}

but *studentInfo was not updated.

You are storing a copy of the value of your const char* pointers into your map, so you are not able to update the original pointers inside the StudentInfo struct. You would have to store the address of the pointers instead, eg:

void foo(StudentInfo *studentInfo, const std::string &key)
{
    std::map<std::string, const char**> studentInfoMap;
    
    studentInfoMap.insert(std::make_pair("name", &(studentInfo->name)));
    studentInfoMap.insert(std::make_pair("address", &(studentInfo->address)));

    for(auto &item : studentInfoMap)
    {
       if (key == item.first)
       {
          *(item.second) = "John";
       }
    }
}

That being said, the for loop is unnecessary. You can use map::operator[] or map::at() to access an element by its key, eg:

void foo(StudentInfo *studentInfo, const std::string &key)
{
    std::map<std::string, const char**> studentInfoMap;
    
    studentInfoMap.insert(std::make_pair("name", &(studentInfo->name)));
    studentInfoMap.insert(std::make_pair("address", &(studentInfo->address)));

    *(studentInfoMap[key]) = "John";
    // or
    *(studentInfoMap.at(key)) = "John";
}

You should also consider using std::string instead of const char* inside of your struct, eg:

struct StudentInfo
{
    int age;
    std::string name;
    std::string address;
};

void foo(StudentInfo *studentInfo, const std::string &key)
{
    std::map<std::string, std::string*> studentInfoMap;
    
    studentInfoMap.insert(std::make_pair("name", &(studentInfo->name)));
    studentInfoMap.insert(std::make_pair("address", &(studentInfo->address)));

    *(studentInfoMap[key]) = "John";
    // or
    *(studentInfoMap.at(key)) = "John";
}