How Can I Iterate Over Nested Maps in C ?

Iterating Over Nested Maps in C

Looping through a map of maps in C can be accomplished using nested for loops. Consider the following container:

std::map<std::string, std::map<std::string, std::string>> m;

// Example data
m["name1"]["value1"] = "data1";
m["name1"]["value2"] = "data2";
m["name2"]["value1"] = "data1";
m["name2"]["value2"] = "data2";
m["name3"]["value1"] = "data1";
m["name3"]["value2"] = "data2";

Nested For Loops:

To iterate over this map, use nested for loops:

for (auto const &ent1 : m) {
  // ent1.first is the outer key
  for (auto const &ent2 : ent1.second) {
    // ent2.first is the inner key
    // ent2.second is the value
  }
}

This approach gives access to the outer key, inner key, and value for each element in the nested map.

C 11 Enhancements:

In C 11, the ranged-based for loop can be used to simplify the above code:

for (auto const &[outer_key, inner_map] : m) {
  for (auto const &[inner_key, inner_value] : inner_map) {
    // Access outer_key, inner_key, and inner_value directly
  }
}

C 17 Structured Bindings:

In C 17, structured bindings can further simplify the syntax:

for (auto const &[outer_key, inner_map] : m) {
  for (auto const &[inner_key, inner_value] : inner_map) {
    // Access outer_key, inner_key, and inner_value without need for variables
  }
}

By using these methods, you can efficiently loop through nested maps and access the data they contain.

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