Problem with Maps!

Posted on 2004-11-01
Last Modified: 2010-04-01
I have quite a few char * arrays of environment variables.....I've listed just a few here..

const char *group4Envs[] = {

const char *group5Envs[] = {

const char *group7Envs[] = {

char *const char *signalTypes[] = {
  "AA1", "CB", "CB1", "T4", "NA1"
i then have a function which gets the env variable which represents the path and filename of a configuration file.  This information is then stored in a map .then  uses a signal type as a key...which is mapped with the configuration files.

the char array for group 7 has 5 env variables in it while the others have 4...

bool ViewForm::checkEnvExists(const char **envList, std::map<std::string, std::string>& groupFiles)
  for (unsigned int i = 0; i < sizeof(envList); i++)
       std::string filename = getenv(envList[i]);
       printf("%s\n", filename.c_str());
       if (filename == NULL)
           printf("Error: %s env not defined\n", envList[i]);
           return false;
       groupFiles[signalTypes[i]] = filename;
  return true;
I call the function for each char * array...

std::map<std::string, std::string> mobileGrp3Files;
    std::map<std::string, std::string> mobileGrp4Files;
    std::map<std::string, std::string> mobileGrp5Files;
    std::map<std::string, std::string> mobileGrp7Files;
   checkEnvExists(group3Envs, mobileGrp3Files)
   checkEnvExists(group4Envs, mobileGrp4Files)
   checkEnvExists(group5Envs, mobileGrp5Files)
   checkEnvExists(group7Envs, mobileGrp7Files)

However, with group7Envs, it only stores 4 entries in the map, when it should be 5.  I know it must be something silly I overlooked.  Why doesn't it store the 5th entry?
Question by:jewee
    1 Comment
    LVL 14

    Accepted Solution

    -->  for (unsigned int i = 0; i < sizeof(envList); i++)

    sizeof() is a compile time construct, in this case you are getting the size (in bytes) of a const char ** pointer, which is 4 (bytes). You are *not* getting the number of strings in the array, and it is not evaluated at run time.

    So your loop will always go through exactly 4 times.

    If one of your arrays has less than 4 strings, your program could crash.

    Rather than using sizeof, I think you have 2 choices:

    1) Add a NULL to the end of the array, and loop through looking for NULL:

    const char *group4Envs[] = {


      int i = 0;
      while (envList[i] != NULL) {

    2) pass in the array size as an argument.

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