Efficiently reading csv file in MQL4?

External question — Stack Overflow Stack Exchange Author: lazarea Original post: https://stackoverflow.com/questions/66806132 License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ Adaptation: HTML converted to plain text; contact email addresses removed. I placed "AAPL.csv" into the MetaTrader terminal folder's Files subfolder (MQL4/Files) to be accessible by the EA. The structure of this csv is as follows: Date,Open,High,Low,Close,Adj Close,Volume 1980-12-12,0.1283479928970337,0.1289059966802597,0.1283479928970337,0.1283479928970337,0.10092189908027649,469033600 1980-12-15,0.12221000343561172,0.12221000343561172,0.12165199965238571,0.12165199965238571,0.09565676748752594,175884800 I want to read this, as well as many other similar csv files. All files have different lengths. My question is, what is the best practice when reading variable-length files? For now, I managed to read the content of my file by creating a 2-dimensional array: string s[7][1000000]; although this is poor programming (what if the file only has 500 rows?) and it can still fail if I encounter a csv that is longer (what if file has 1000001 rows?). I tried using a dynamic array: string s[7][]; but it returns '[' - invalid index value error. Yet another idea I had to use the FileSize() function and allocate just-the-necessary amount of memory to the 2-dimensional array. However, int handle=FileOpen(FileName,FILE_CSV|FILE_READ,","); if(handle>0) { int size = FileSize(handle); ... yielded a size that equals the product of column numbers and row numbers. I was hoping to obtain a row_count and col_count and use them to define s: string s[col_count][row_count]; My full working code: extern string FileName = "AAPL.csv"; int init() { int row=0,col=0; string s[7][1000000]; ResetLastError(); int handle=FileOpen(FileName,FILE_CSV|FILE_READ,","); if(handle>0) { while(True) { string temp = FileReadString(handle); if(FileIsEnding(handle)) break; //FileIsEnding = End of File s[col][row]=temp; if(FileIsLineEnding(handle)) //FileIsLineEnding = End of Line { col = 0; //reset col = 0 for the next row row++; //next row } else { col++; //next col of the same row } } FileClose(handle); } else { Comment("File "+FileName+" not found, the last error is ", GetLastError()); } return(0); } int start() { return(0); }

External answer — Stack Overflow Stack Exchange Author: PaulB Original post: https://stackoverflow.com/a/66905503 License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ Adaptation: HTML converted to plain text; contact email addresses removed. You should use the first dimension of the array for your rows and the second dimension for your columns. You would therefore have an array statement of string s[1][7]; You can then resize your array as you loop through reading your csv file as follows: string s[1][7]; int handle=FileOpen(FileName,FILE_CSV|FILE_READ,","); if(handle==INVALID_HANDLE) Print("Error opening file ",GetLastError()); else { int row=0; while(!FileIsEnding(handle)) { if(row>0) ArrayResize(s,row+1); //carry out array reading here //eg s[row][0]=FileReadString(handle); //eg s[row][1]=FileReadString(handle); //etc row++; } FileClose(handle); } You can not resize the 2nd dimension of a multi dimensional array.

External answer — Stack Overflow Stack Exchange Author: Sean Champ Original post: https://stackoverflow.com/a/76973571 License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ Adaptation: HTML converted to plain text; contact email addresses removed. For what it's worth, dingmaotu has published mql4-lib at GitHub. This API offers a number of useful MQL classes and functions, including support for file I/O in MQL4. The README file provides an example of writing a CSV file with the API. It works - tested locally for CSV output from custom indicator data.