Here are five possible code completions for the given code snippet, each addressing the CWE-125 vulnerability (Out-of-bounds Read) in a different way:

**1. Input Validation with Error Handling**
```c
int
main (int argc, char **argv)
{
  int limit;
  if (argc < 2) {
    fprintf(stderr, "Error: missing argument\n");
    return 1;
  }
  limit = atoi(argv[1]);
  if (limit <= 0) {
    fprintf(stderr, "Error: invalid limit\n");
    return 1;
  }
  // ...
}
```
In this example, we check if the user provided a command-line argument and if the argument is a positive integer. If not, we print an error message and exit the program.

**2. Input Validation with Default Value**
```c
int
main (int argc, char **argv)
{
  int limit = 10; // default value
  if (argc > 1) {
    limit = atoi(argv[1]);
    if (limit <= 0) {
      limit = 10; // use default value if invalid input
    }
  }
  // ...
}
```
In this example, we set a default value for the `limit` variable and only update it if the user provided a valid command-line argument.

**3. Using strtol() for Safe Integer Conversion**
```c
int
main (int argc, char **argv)
{
  int limit;
  if (argc < 2) {
    fprintf(stderr, "Error: missing argument\n");
    return 1;
  }
  char *endptr;
  limit = strtol(argv[1], &endptr, 10);
  if (endptr == argv[1] || *endptr != '\0') {
    fprintf(stderr, "Error: invalid limit\n");
    return 1;
  }
  if (limit <= 0) {
    fprintf(stderr, "Error: invalid limit\n");
    return 1;
  }
  // ...
}
```
In this example, we use the `strtol()` function to safely convert the command-line argument to an integer. We also check for errors and invalid input.

**4. Using sscanf() for Safe Integer Conversion**
```c
int
main (int argc, char **argv)
{
  int limit;
  if (argc < 2) {
    fprintf(stderr, "Error: missing argument\n");
    return 1;
  }
  if (sscanf(argv[1], "%d", &limit) != 1) {
    fprintf(stderr, "Error: invalid limit\n");
    return 1;
  }
  if (limit <= 0) {
    fprintf(stderr, "Error: invalid limit\n");
    return 1;
  }
  // ...
}
```
In this example, we use the `sscanf()` function to safely convert the command-line argument to an integer. We also check for errors and invalid input.

**5. Using a Safe Integer Conversion Function**
```c
int safe_atoi(const char *str) {
  int value;
  if (sscanf(str, "%d", &value) != 1) {
    return -1; // error
  }
  return value;
}

int
main (int argc, char **argv)
{
  int limit;
  if (argc < 2) {
    fprintf(stderr, "Error: missing argument\n");
    return 1;
  }
  limit = safe_atoi(argv[1]);
  if (limit <= 0) {
    fprintf(stderr, "Error: invalid limit\n");
    return 1;
  }
  // ...
}
```
In this example, we define a `safe_atoi()` function that safely converts a string to an integer using `sscanf()`. We then use this function in the `main()` function to convert the command-line argument to an integer.