Call c_str() function from String class for upload file txt to storage

Projects General Guidance
1

I've tried the File Upload program to upload files stored on the SD Card to Firebase Storage and it worked fine. then due to a datalogger need, I created a dynamic file naming system function based on month-day on RTC. then the format of the file name is created in a string. when I try again it causes an error in the upload process when I create an upload function like this. When FileName variable used as localFileName and remoteFilename in the upload function, which required const char*, need to call c_str() function from String class. FileName.c_str()need help with this, How to call the String FileName that i had created and write it for syntax?

DateTime now = rtc.now();
  FileName[0] = now.day()/10 + '0';
  FileName[1] = now.day()%10 + '0';
  dayupg=now.day();
  FileName[2] = now.month()/10 + '0';
  FileName[3] = now.month()%10 + '0';
  monthupg=now.month();
  FileName[4] = (now.year()/10)%10 + '0';
  FileName[5] = now.year()%10 + '0';
  yearupg=now.year();

  if (Firebase.ready() && currentTime - timeStorage >= intervalStorage)
  {  
    Serial.print("Upload file : ");
    Serial.println(FileName);
    if (Firebase.Storage.upload(&fbdo, STORAGE_BUCKET_ID, String("/" + FileName).c_str(), mem_storage_type_sd, FileName.c_str(), "data.txt"))
      Serial.printf("\nDownload Link: %s\n", fbdo.downloadURL().c_str());
    else
      Serial.println(fbdo.errorReason());
    timeStorage = currentTime;
  }

the error :

1017×231 8.53 KB

** error: invalid operands of types 'const char [2]' and 'char [11]' to binary 'operator+'
278 | if (Firebase.Storage.upload(&fbdo, STORAGE_BUCKET_ID, String("/" + FileName).c_str(), mem_storage_type_sd, FileName.c_str(), "data.txt"))
| ~~~ ^ ~~~~~~~~
| | |
| | char [11]
| const char [2]
error: request for member 'c_str' in 'FileName', which is of non-class type 'char [11]'
278 | if (Firebase.Storage.upload(&fbdo, STORAGE_BUCKET_ID, String("/" + FileName).c_str(), mem_storage_type_sd, FileName.c_str(), "data.txt"))
| ^~~~~
exit status 1
invalid operands of types 'const char [2]' and 'char [11]' to binary 'operator+'**

2

Welcome,

There is no need to convert a C-string to a String then back to a C-string. Use functions strcat or sprintf instead. Here is an example : OAfVZy - Online C++ Compiler & Debugging Tool - Ideone.com

1 Like
3

the + operator only works on Strings not char[ ]s. The problem is FileName is NOT an Arduino String but a char [11]
so do

String fileNameStr = "/";
fileNameStr += FileName;
if (Firebase.Storage.upload(&fbdo, STORAGE_BUCKET_ID, fileNameStr .c_str(), mem_storage_type_sd, FileName, "data.txt"))

P.s. if you want to use strcat don't, use strlcat instead it is much safer for an example of using strlcat see strlcpy_strlcat.ino
Don't use sprintf either see C static code analysis for the snprintf safer alternative and https://joequery.me/code/snprintf-c/

4

thanks for replying, the link you provided helped me to understand about string class

5

I applied whatever example you gave, and it works according to what I expected
String fileNameStr = "/"; fileNameStr += FileName; if (Firebase.Storage.upload(&fbdo, STORAGE_BUCKET_ID, fileNameStr .c_str(), mem_storage_type_sd, FileName, "data.txt"))

thanks for helping!

6

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