I have 4 columns with long text in each column. The text overflows to next column if tried below code:
]1
\documentclass{article}
\usepackage{longtable}
\usepackage{multirow}
\title{A longtable example}
\begin{document}
\begin{center}
\begin{longtable}{p{2.8cm} p{2.8cm}p{2.8cm}p{2.8cm}}
\caption{A sample long table.} \label{tab:long} \\
\hline \multicolumn{1}{c}{\textbf{First column}} & \multicolumn{1}{c}{\textbf{Second column}} & \multicolumn{1}{c}{\textbf{Third column}}&
\multicolumn{1}{c}{\textbf{TForth column}}\\ \hline
\endfirsthead
\multirow{4}{c}%
{{\bfseries \tablename\ \thetable{} -- continued from previous page}} \\
\hline \multicolumn{1}{c}{\textbf{Reference}} & \multicolumn{1}{c}{\textbf{techniqued}} & \multicolumn{1}{c}{\textbf{issues}}
\multicolumn{1}{c}{\textbf{future}}\\ \hline
\endhead
\hline \multicolumn{4}{r}{{Continued on next page}} \\ \hline
\endfoot
\hline \hline
\endlastfoot
\multirow{4}{*} textttttttttttttttttttttttt & abcdef ghjijklmn & 123.456778 & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
One & abcdef ghjijklmn & 123.456778 \\
\end{longtable}
\end{center}
\end{document}][1]][1]
I want to restrict long text to each specific column.

textttttttttttttttttttttttt. In your opinion, how and where should this string be line-broken? Please advise. – Mico Feb 05 '20 at 12:32textttttttttttttttttttttttttttwith some real words that have spaces between them: you will find that LaTeX will keep everything within the space for that column in that case. If you need to tell LaTeX exactly where to break the line, then you can use\newline. – rbrignall Feb 05 '20 at 12:34longtableenvironment should never, ever be encased in acenterenvironment. – Mico Feb 05 '20 at 12:35longtabledoes the centering of its contents itself andcentergives inconsistent spacing above and below thelongtable. – Skillmon Feb 05 '20 at 12:44longtableenvironment centers its contents automatically. Encasing alongtablein acenterenvironment achieves nothing except that it inserts unneeded and unwanted whitespace above and below thelongtablematerial. Quite a few postings on this site make this point; see, for instance, my comment under the posting how to have a caption on top of longtable. – Mico Feb 05 '20 at 12:56centerandlongtableenvironments was not the main subject of your query. Unfortunately, that comment subsequently got hijacked and blown out of all proportion. Anyway, do please provide some information about how you believe the stringtextttttttttttttttttttttttt(or all other strings whose widths exceed the width of the cell) should be line-broken. – Mico Feb 06 '20 at 11:45