本人在用vs+qt编写日志功能，其中 FindID()为返回目前案例编号
```c++
void QtWidgetsApplication3::UPfile()
{
file.setFileName(path);
if(file.open(QIODevice::Append | QIODevice::Text))
qDebug() << "UPfile被执行" << endl;
QDateTime dateTime = QDateTime::currentDateTime();//获取系统当前的时间
ID = FindID().toInt()+1;
QString str = QString::number(ID)+ ":" + dateTime.toString("yyyy-MM-dd hh-mm-ss") + ";";//格式化时间
qDebug() << "str:"<//正常
if (ID > 30)
{
QMessageBox::information
(this, tr("日志超出储存范围"), tr("日志仅支持记录30条"));
file.close();
file.open(QIODevice::ReadWrite);
file.write("编号：年-月-日-时-分-秒-WB-PPP-RBC-PRP;");
file.close();
file.open(QIODevice::Append);
ID = 1;
str = QString::number(ID) + ":" + dateTime.toString("yyyy-MM-dd hh-mm-ss") + ";";//格式化时间
}
else
{
QMessageBox::information
(this, tr("储存日志"), tr("储存日志成功"));
}
QTextStream stream(&file);
stream << str;
qDebug() << "添加日志";
file.close();
}
调试输出
```c++
UPfile被执行
QFile::setFileName: File (D:/Qt/QtProgram/cprp/QtWidgetsApplication3 - 2/QtWidgetsApplication3/������־.txt) is already opened
lineStr: "缂栧彿锛氬勾-鏈鏃鏃鍒绉WB-PPP-RBC-PRP;" 1
lineStr: "30锛" 2
lineStr: "1:2023-02-22 15-00-10;" 3
":" 0.1
str: "2:2023-02-22 15-00-16;"
添加日志
QIODevice::write (QFile, "D:\Qt\QtProgram\cprp\QtWidgetsApplication3 - 2\QtWidgetsApplication3\病例日志.txt"): ReadOnly device
锛其实是冒号
运行前txt内容为
编号：年-月-日-时-分-秒-WB-PPP-RBC-PRP;
30：
运行后txt内容为
编号：年-月-日-时-分-秒-WB-PPP-RBC-PRP;
30：
1:2023-02-22 15-00-10;
问题在于写入操作只有ID超出设定范围时生效，且也不是我设想的重新编写，而是在文档后面追加。
去掉if体的话连超出设定都不会生效，一天了都没搞明白为什么，求指点迷津，ORL
直接用我这款久经考验的土造MyLog，原因不解释！
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#ifdef _MSC_VER
#pragma warning(disable:4996)
#include <windows.h>
#include <io.h>
#else
#include <unistd.h>
#include <sys/time.h>
#include <pthread.h>
#define CRITICAL_SECTION pthread_mutex_t
#define _vsnprintf vsnprintf
#endif
//Log{
#define MAXLOGSIZE 20000000
#define MAXLINSIZE 16000
#include <time.h>
#include <sys/timeb.h>
#include <stdarg.h>
char logfilename1[]="MyLog1.log";
char logfilename2[]="MyLog2.log";
static char logstr[MAXLINSIZE+1];
char datestr[16];
char timestr[16];
char mss[4];
CRITICAL_SECTION cs_log;
FILE *flog;
#ifdef _MSC_VER
void Lock(CRITICAL_SECTION *l) {
EnterCriticalSection(l);
}
void Unlock(CRITICAL_SECTION *l) {
LeaveCriticalSection(l);
}
#else
void Lock(CRITICAL_SECTION *l) {
pthread_mutex_lock(l);
}
void Unlock(CRITICAL_SECTION *l) {
pthread_mutex_unlock(l);
}
#endif
void LogV(const char *pszFmt,va_list argp) {
struct tm *now;
struct timeb tb;
if (NULL==pszFmt||0==pszFmt[0]) return;
_vsnprintf(logstr,MAXLINSIZE,pszFmt,argp);
ftime(&tb);
now=localtime(&tb.time);
sprintf(datestr,"%04d-%02d-%02d",now->tm_year+1900,now->tm_mon+1,now->tm_mday);
sprintf(timestr,"%02d:%02d:%02d",now->tm_hour ,now->tm_min ,now->tm_sec );
sprintf(mss,"%03d",tb.millitm);
printf("%s %s.%s %s",datestr,timestr,mss,logstr);
flog=fopen(logfilename1,"a");
if (NULL!=flog) {
fprintf(flog,"%s %s.%s %s",datestr,timestr,mss,logstr);
if (ftell(flog)>MAXLOGSIZE) {
fclose(flog);
if (rename(logfilename1,logfilename2)) {
remove(logfilename2);
rename(logfilename1,logfilename2);
}
} else {
fclose(flog);
}
}
}
void Log(const char *pszFmt,...) {
va_list argp;
Lock(&cs_log);
va_start(argp,pszFmt);
LogV(pszFmt,argp);
va_end(argp);
Unlock(&cs_log);
}
//Log}
int main(int argc,char * argv[]) {
int i;
#ifdef _MSC_VER
InitializeCriticalSection(&cs_log);
#else
pthread_mutex_init(&cs_log,NULL);
#endif
for (i=0;i<10000;i++) {
Log("This is a Log %04d from FILE:%s LINE:%d\n",i, __FILE__, __LINE__);
}
#ifdef _MSC_VER
DeleteCriticalSection(&cs_log);
#else
pthread_mutex_destroy(&cs_log);
#endif
return 0;
}
//1-79行添加到你带main的.c或.cpp的那个文件的最前面
//82-86行添加到你的main函数开头
//90-94行添加到你的main函数结束前
//在要写LOG的地方仿照第88行的写法写LOG到文件MyLog1.log中