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Altering the string returned by strerror() results in undefined behavior.

Noncompliant Code Example (getenv())

This noncompliant code example modifies the string returned by getenv() by replacing all double quote (") characters with underscores.

void trstr(char *str, char orig, char rep) {
  while (*str != '\0') {
    if (*str == orig) {
      *str = rep;
    }
    str++;
  }
}

/* ... */

char *env = getenv("TEST_ENV");
if (env == NULL) {
  /* Handle error */
}

trstr(env,'"', '_');


/* ... */

Compliant Solution (getenv()) (local copy)

For the case where the intent of the noncompliant code example is to use the modified value of the environment variable locally and not modify the environment, this compliant solution makes a local copy of that string value and then modifies the local copy.

const char *env;
char *copy_of_env;

env = getenv("TEST_ENV");
if (env == NULL) {
  /* Handle error */
}

copy_of_env = (char *)malloc(strlen(env) + 1);
if (copy_of_env == NULL) {
  /* Handle error */
}

strcpy(copy_of_env, env);
trstr(copy_of_env,'\"', '_');

Compliant Solution (getenv()) (Modifying the Environment in POSIX)

For the case where the intent is to modify the environment, this compliant solution saves the altered string back into the environment by using the POSIX setenv() and strdup() functions.

const char *env;
char *copy_of_env;

env = getenv("TEST_ENV");
if (env == NULL) {
  /* Handle error */
}

copy_of_env = strdup(env);
if (copy_of_env == NULL) {
  /* Handle error */
}

trstr(copy_of_env,'\"', '_');

if (setenv("TEST_ENV", copy_of_env, 1) != 0) {
  /* Handle error */
}

Noncompliant Code Example (setlocale())

This noncompliant code example modifies the string returned by setlocale() by terminating the string when '.' is encountered such as “en_US.iso88591” to “en_US”. In this case, the behavior is undefined.

void terminate_on_dot(char *str){
  int i;

  for (i = 0; i < strlen(locale); i++){
    if(locale[i] == '.'){
      locale[i] = ‘\0’;
      break;
    }
  }
}

/* ... */

char *locale = setlocale(LC_ALL, "");
if (locale == NULL) {
  /* Handle error */
}

terminate_on_dot(locale);

/* ... */

Compliant Solution (setlocale())

Similar to the case of getenv(), this compliant solution makes a local copy of that string value and then modifies the local copy.

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