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Querying Object Content

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Last updated: 2026-03-05 17:03:30

Introduction

This document introduces the sample code and description for searching object content via the C++ SDK in COS.

Must-Knows

To use the feature of retrieving object content, you must have read permission for the target object. When configuring authorization policies, set the action to cos:GetObject. For more authorization details, see CAM-supported APIs.
COS Select supports searching object data in the following formats:
CSV format: Objects are stored in CSV format and delimited by specific separators.
JSON format: Objects are stored in JSON format, which can be either JSON files or JSON lists.
CSV and JSON objects must be encoded in UTF-8 format.
COS Select supports searching GZIP or BZIP2 compressed CSV and JSON objects.
COS Select supports searching SSE-COS encrypted CSV and JSON objects.

Related Examples

Function Name
Description
Example code
Querying Object Content
Using Structured Query Language (SQL) to search content from specified objects (in CSV, JSON, or Parquet format).

Preliminary Preparation

Create CosAPI

Before calling the COS API, you must first create an instance of CosAPI to make subsequent call requests.
qcloud_cos::CosAPI InitCosAPI() {
    uint64_t appid = 12500000000;
    std::string region = "ap-guangzhou";// Region of the bucket, see https://www.tencentcloud.com/document/product/436/62?from_cn_redirect=1
    std::string secret_id = "************************************"; // User's SecretId. It is recommended to use sub-account keys, with authorization following the least privilege principle to mitigate usage risks. For information on how to obtain sub-account keys, see https://www.tencentcloud.com/document/product/598/37140?from_cn_redirect=1
    std::string secret_key = "************************************"; // User's SecretKey. It is recommended to use sub-account keys, with authorization following the least privilege principle to mitigate usage risks. For information on how to obtain sub-account keys, see https://www.tencentcloud.com/document/product/598/37140?from_cn_redirect=1
        
    qcloud_cos::CosConfig config(appid, secret_id, secret_key, region);
    qcloud_cos::CosAPI cos_tmp(config);
    return cos_tmp;
}

Create CosAPI Using a Temporary Key

To access COS with a temporary key, you need to create a CosAPI instance using the temporary key.
qcloud_cos::CosAPI InitCosAPI() {
    // You need to have obtained the temporary key results: tmp_secret_id, tmp_secret_key,
    // For generating temporary keys, see https://www.tencentcloud.com/document/product/436/14048?from_cn_redirect=1#cos-sts-sdk
    uint64_t appid = 12500000000;
    std::string region = "ap-guangzhou";
    std::string tmp_secret_id = "************************************";
    std::string tmp_secret_key = "************************************";
    std::string tmp_token = "token";
    
    qcloud_cos::CosConfig config(appid, tmp_secret_id, tmp_secret_key, region);
    config.SetTmpToken(tmp_token);
    qcloud_cos::CosAPI cos_tmp(config);
    return cos_tmp;
}

Use Cases

Search CSV Format

Method Prototype

CosResult CosAPI::SelectObjectContent(const SelectObjectContentReq& req, SelectObjectContentResp* resp)

Request Example

void SelectObjectContentDemo(qcloud_cos::CosAPI& cos) {
    std::string object_name = "test.csv.gz";
    int input_file_type = CSV;                // The format of the object to be searched is CSV or JSON
    int input_compress_type = COMPRESS_GZIP;  // Compression type: COMPRESS_NONE, COMPRESS_GZIP, COMPRESS_BZIP2
    int out_file_type = CSV;                  // The output format is CSV or JSON

    qcloud_cos::SelectObjectContentReq req(bucket_name, object_name, input_file_type, input_compress_type, out_file_type);
    req.SetSqlExpression("Select * from COSObject");
    qcloud_cos::SelectObjectContentResp resp;
    qcloud_cos::CosResult result = cos.SelectObjectContent(req, &resp);

    std::cout << "=====================IsObjectExist=======================" << std::endl;
    PrintResult(result, resp);
    // Supports printing the final results to the terminal or writing to a local file.
    // resp.WriteResultToLocalFile("file_name");
    resp.PrintResult();
    std::cout << "=========================================================" << std::endl;
}

Parameter Description

Parameter Name
Description
Type
req
Search Objects Request
SelectObjectContentReq
resp
Search Objects Response
SelectObjectContentResp
SelectObjectContentReq Member or Function Description:
Member or Function
Description
Parameter Type
bucket_name
Bucket name, which can be set via the constructor or set method.
The naming format for buckets is BucketName-APPID. For details, see Naming Conventions
string
object_name
Object key (Key), which can be set via the constructor or set method.
is the unique identifier of the object in the bucket. For example, in the object access domain name examplebucket-1250000000.cos.ap-guangzhou.myqcloud.com/doc/picture.jpg, the object key is doc/picture.jpg. For details, see Object Key
string
input_file_type
The format of the object to be searched can be set via the constructor or set method.
string
input_compress_type
Compression type, which can be set via the constructor or set method.
string
out_file_type
Output format, which can be set via the constructor or set method.
string
SelectObjectContentResp Member Function Description:
Member functions
Description
Return Type
PrintResult
Print the final results to the terminal.
None
WriteResultToLocalFile
Write the final results to a local file.
None
GetXCosRequestId
Obtain the request ID
string

Returning Description

CosResult main member functions are as follows:
Member functions
Description
Return Type
IsSucc
Indicates whether the operation is successful; returns true for success, false for failure.
bool
GetHttpStatus
Obtain the http status code.
int
GetErrorCode
The error code can be obtained when the request fails.
string
GetErrorMsg
Obtain the error message when the request fails.
string
GetXCosRequestId
Obtain the request ID.
string
Usage examples for CosResult are as follows. Users may choose to utilize them based on their needs:
void PrintResult(const qcloud_cos::CosResult& result, const qcloud_cos::BaseResp& resp) {
    if (result.IsSucc()) {
        std::cout << "Request Succ." << std::endl;
        std::cout << resp.DebugString() << std::endl;
    } else {
        std::cout << "ErrorMsg=" << result.GetErrorMsg() << std::endl;
        std::cout << "HttpStatus=" << result.GetHttpStatus() << std::endl;
        std::cout << "ErrorCode=" << result.GetErrorCode() << std::endl;
        std::cout << "ErrorMsg=" << result.GetErrorMsg() << std::endl;
        std::cout << "ResourceAddr=" << result.GetResourceAddr() << std::endl;
        std::cout << "XCosRequestId=" << result.GetXCosRequestId() << std::endl;
        std::cout << "XCosTraceId=" << result.GetXCosTraceId() << std::endl;
    }
}

API Operations

For the API description related to searching object content, see the SELECT Object Content document.
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