How to reply particular mail in c using gmail api

To reply to a particular email using the Gmail API in C, you'll need to follow these steps:

Prerequisites

Create a project in the Google Cloud Console and enable the Gmail API.
Create credentials for your project (OAuth client ID).
Install the Google API Client Library for C.

Step 1: Set up the Gmail API

Import the necessary headers:

#include <google/api_core.grpc.pb.h>
#include <google/api_core/util.h>
#include <google/auth/oauth2.h>
#include <google/gmail/v1/gmail_service.grpc.pb.h>

Initialize the Gmail API client:


// Replace with your project ID and credentials
const char* kProjectId = "your-project-id";
const char* kClientId = "your-client-id";
const char* kClientSecret = "your-client-secret";
const char* kRedirectUri = "urn:ietf:wg:oauth:2.0:oob";

// Initialize the OAuth2 credentials google::auth::OAuth2Credentials credentials(kClientId, kClientSecret, kRedirectUri);

// Create the Gmail API client google::gmail::v1::GmailServiceClient* client = new google::gmail::v1::GmailServiceClient( credentials, google::api_core::grpc::ChannelPool::CreateDefaultPool());

**Step 2: Retrieve the email message**

1. Use the `users.messages.list` method to retrieve the email message:
```c
// Replace with the email ID and user ID
const char* kEmailId = "your-email-id";
const char* kUserId = "your-user-id";

google::gmail::v1::ListMessagesRequest request;
request.setUserId(kUserId);
request.setLabelIds({"INBOX"});

google::gmail::v1::ListMessagesResponse response;
client->ListMessages(request, &response);

// Find the email message with the desired ID
for (const auto& message : response.getMessages()) {
    if (strcmp(message.getId(), kEmailId) == 0) {
        // Found the email message, proceed to reply
        break;
    }
}

Step 3: Compose the reply

Create a new Message object:

google::gmail::v1::Message reply;
reply.setThreadId(message.getThreadId());
reply.setLabelIds({"INBOX"});

Set the reply text:

google::protobuf::TextFormat::ParseString(reply.mutableBody(), "Your reply text here");

Step 4: Send the reply

Use the users.messages.send method to send the reply:


google::gmail::v1::SendMessageRequest request;
request.setUserId(kUserId);
request.setMessage(&reply);

client->SendMessage(request, nullptr);

**Full code example**

Here's the complete code example:
```c
#include <google/api_core/grpc.pb.h>
#include <google/api_core/util.h>
#include <google/auth/oauth2.h>
#include <google/gmail/v1/gmail_service.grpc.pb.h>

int main() {
    // Set up the Gmail API
    const char* kProjectId = "your-project-id";
    const char* kClientId = "your-client-id";
    const char* kClientSecret = "your-client-secret";
    const char* kRedirectUri = "urn:ietf:wg:oauth:2.0:oob";

    google::auth::OAuth2Credentials credentials(kClientId, kClientSecret, kRedirectUri);

    google::gmail::v1::GmailServiceClient* client = new google::gmail::v1::GmailServiceClient(
        credentials, google::api_core::grpc::ChannelPool::CreateDefaultPool());

    // Retrieve the email message
    const char* kEmailId = "your-email-id";
    const char* kUserId = "your-user-id";

    google::gmail::v1::ListMessagesRequest request;
    request.setUserId(kUserId);
    request.setLabelIds({"INBOX"});

    google::gmail::v1::ListMessagesResponse response;
    client->ListMessages(request, &response);

    for (const auto& message : response.getMessages()) {
        if (strcmp(message.getId(), kEmailId) == 0) {
            // Found the email message, proceed to reply
            break;
        }
    }

    // Compose the reply
    google::gmail::v1::Message reply;
    reply.setThreadId(message.getThreadId());
    reply.setLabelIds({"INBOX"});

    google::protobuf::TextFormat::ParseString(reply.mutableBody(), "Your reply text here");

    // Send the reply
    google::gmail::v1::SendMessageRequest request;
    request.setUserId(kUserId);
    request.setMessage(&reply);

    client->SendMessage(request, nullptr);

    return 0;
}

Note that this code example assumes you have already set up the Gmail API and have the necessary credentials. You'll need to modify the code to fit your specific use case and handle errors properly.

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How to reply particular mail in c using gmail api