Qt中怎样读取文件指定的行？

Posted 2023-04-04

你提到行,很明显你要操作的是文本文件,文本文件是顺序文件,只能用
QFile file("FileName");
QTextStream in(&file);
int i=0;
QString line="";
while (!in.atEnd() && ++i<=lineNo )
line=in.readLine();

其它用途请用随机存储! 参考技术A 1、qint64 QFile::readLineData ( char * data, qint64 maxlen )
[virtual protected]
Reimplemented from QIODevice::readLineData().

2、qint64 QIODevice::readLine ( char * data, qint64 maxSize )
This function reads a line of ASCII characters from the device, up to a maximum of maxSize - 1 bytes, stores the characters in data, and returns the number of bytes read. If a line could not be read but no error ocurred, this function returns 0. If an error occurs, this function returns the length of what could be read, or -1 if nothing was read.
A terminating '\0' byte is always appended to data, so maxSize must be larger than 1.
Data is read until either of the following conditions are met:
The first '\n' character is read.
maxSize - 1 bytes are read.
The end of the device data is detected.
For example, the following code reads a line of characters from a file:
QFile file("box.txt");
if (file.open(QFile::ReadOnly))
char buf[1024];
qint64 lineLength = file.readLine(buf, sizeof(buf));
if (lineLength != -1)
// the line is available in buf



3、QByteArray QIODevice::readLine ( qint64 maxSize = 0 )
This is an overloaded function.
Reads a line from the device, but no more than maxSize characters, and returns the result as a QByteArray.
This function has no way of reporting errors; returning an empty QByteArray() can mean either that no data was currently available for reading, or that an error occurred. 参考技术B QFile file(srcDir);
if (file.open(QIODevice::ReadOnly | QIODevice::Text))

int row=0;
while (!file.atEnd())

QByteArray line = file.readLine();
if(++row==2)
//QString a=file.readLine();
QString str(line);
qDebug() << str;


file.close();

shell 读取连续指定文件的行输入到另一个文件中

#!/bin/bash
a=3975
lines=`wc -l /tmp/zabbix_proxy.log | awk ‘{print $1}‘`
echo $a:$lines
for ((i=$a;i<=$lines;i++))
do
    n=$[i]p
    cmd="sed -n $n /tmp/zabbix_proxy.log"
    echo $i:$n
    $cmd
done