char * 与 string 类型相互转换方法--Linux C/C++

本文介绍如何在C++中将C风格的字符串(如char*和char数组)转换为string类型,以及如何从string类型获取C风格的字符串。包括直接类型转换和使用string的c_str()方法。

1:对于C风格的字符串比如char*,char str[],转换为 string

         char * 和char str[]类型可以直接转换为string 类型;

          即,在char * chstr,

                      char arstr[]

                      string str=chstr;或者是string str=arstr;可以直接进行赋值。

2:对于string 转换为char *

     string提供一个方法可以直接返回字符串的首指针地址即:string.c_str();

     比如:string str="Hi Cpp";转换为char * 类型;

     const char * mystr=str.c_str();  注意要加上const.

 

      例外有个方法有点浪费内存:

     string str="woshi";

     char * pstr=new char [str.length()+1];

     strcat(pstr,str);

 

 

22:19:28: 为项目keypad执行步骤 ... 22:19:28: 正在启动 "/usr/bin/make" clean rm -f moc_predefs.h rm -f moc_keytest.cpp rm -f ui_keytest.h rm -f keytest.o main.o moc_keytest.o rm -f *~ core *.core 22:19:28: 进程"/usr/bin/make"正常退出。 22:19:28: 配置没有改变, 跳过 qmake 步骤。 22:19:28: 正在启动 "/usr/bin/make" /opt/aarch64-buildroot-linux-gnu_sdk-buildroot/bin/uic ../keyScan/keytest.ui -o ui_keytest.h /opt/aarch64-buildroot-linux-gnu_sdk-buildroot/bin/aarch64-buildroot-linux-gnu-g++ -c -pipe -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -g0 -D_FORTIFY_SOURCE=1 --sysroot=/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot -Wall -Wextra -D_REENTRANT -fPIC -DQT_QML_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -I../keyScan -I. -I../keyScan -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/opencv4 -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/qt5 -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/qt5/QtWidgets -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/qt5/QtGui -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/qt5/QtCore -I. -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/libdrm -I. -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/mkspecs/devices/linux-buildroot-g++ -o keytest.o ../keyScan/keytest.cpp ../keyScan/keytest.cpp: 在构造函数‘Keytest::Keytest(QWidget*)’中: ../keyScan/keytest.cpp:161:13: 警告: 语句不起作用 [-Wunused-value] 161 | ui->mainLayout; | ~~~~^~~~~~~~~~ ../keyScan/keytest.cpp: 在函数‘char* scan_devices()’中: ../keyScan/keytest.cpp:147:17: 警告: ignoring return value of ‘int asprintf(char**, const char*, ...)’ declared with attribute ‘warn_unused_result’ [-Wunused-result] 147 | asprintf(&filename, "%s/%s%d", | ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~ 148 | DEV_INPUT_EVENT, EVENT_DEV_NAME, | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 149 | devnum); | ~~~~~~~ ../keyScan/keytest.cpp: 在成员函数‘void Keytest::keyEvent()’中: ../keyScan/keytest.cpp:424:26: 警告: ignoring return value of ‘ssize_t write(int, const void*, size_t)’ declared with attribute ‘warn_unused_result’ [-Wunused-result] 424 | write(g_igpiofd,SYSFS_GPIO_LED_VAL_H,sizeof(SYSFS_GPIO_LED_VAL_H)); // | ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ../keyScan/keytest.cpp:426:27: 警告: ignoring return value of ‘int system(const char*)’ declared with attribute ‘warn_unused_result’ [-Wunused-result] 426 | system("echo 1 > value"); | ~~~~~~^~~~~~~~~~~~~~~~~~ ../keyScan/keytest.cpp:431:26: 警告: ignoring return value of ‘ssize_t write(int, const void*, size_t)’ declared with attribute ‘warn_unused_result’ [-Wunused-result] 431 | write(g_igpiofd,SYSFS_GPIO_LED_VAL_L,sizeof(SYSFS_GPIO_LED_VAL_L)); // | ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ../keyScan/keytest.cpp:433:27: 警告: ignoring return value of ‘int system(const char*)’ declared with attribute ‘warn_unused_result’ [-Wunused-result] 433 | system("echo 0 > value"); | ~~~~~~^~~~~~~~~~~~~~~~~~ ../keyScan/keytest.cpp: 在构造函数‘Keytest::Keytest(QWidget*)’中: ../keyScan/keytest.cpp:127:37: 警告: ‘%s’ directive output may be truncated writing up to 255 bytes into a region of size 53 [-Wformat-truncation=] 127 | "%s/%s", DEV_INPUT_EVENT, namelist[i]->d_name); | ^~ In file included from /opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/stdio.h:906, from /opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/include/c++/12.3.0/cstdio:42, from /opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/include/c++/12.3.0/ext/string_conversions.h:43, from /opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/include/c++/12.3.0/bits/basic_string.h:3968, from /opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/include/c++/12.3.0/string:53, from /opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/qt5/QtCore/qbytearray.h:52, from /opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/qt5/QtCore/qstring.h:50, from /opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/qt5/QtCore/qobject.h:47, from /opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/qt5/QtWidgets/qwidget.h:45, from /opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/qt5/QtWidgets/qdialog.h:44, from /opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/qt5/QtWidgets/qmessagebox.h:45, from ../keyScan/keytest.cpp:3: 在函数‘int snprintf(char*, size_t, const char*, ...)’中, 内联自‘char* scan_devices()’于 ../keyScan/keytest.cpp:126:11, 内联自‘Keytest::Keytest(QWidget*)’于 ../keyScan/keytest.cpp:184:33: /opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/bits/stdio2.h:54:35: 附注: ‘__builtin_snprintf’ output between 12 and 267 bytes into a destination of size 64 54 | return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1, | ~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 55 | __glibc_objsize (__s), __fmt, | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 56 | __va_arg_pack ()); | ~~~~~~~~~~~~~~~~~ /opt/aarch64-buildroot-linux-gnu_sdk-buildroot/bin/aarch64-buildroot-linux-gnu-g++ -c -pipe -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -g0 -D_FORTIFY_SOURCE=1 --sysroot=/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot -Wall -Wextra -D_REENTRANT -fPIC -DQT_QML_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -I../keyScan -I. -I../keyScan -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/opencv4 -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/qt5 -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/qt5/QtWidgets -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/qt5/QtGui -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/qt5/QtCore -I. -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/libdrm -I. -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/mkspecs/devices/linux-buildroot-g++ -o main.o ../keyScan/main.cpp /opt/aarch64-buildroot-linux-gnu_sdk-buildroot/bin/aarch64-buildroot-linux-gnu-g++ -pipe -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -g0 -D_FORTIFY_SOURCE=1 --sysroot=/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot -Wall -Wextra -dM -E -o moc_predefs.h /opt/aarch64-buildroot-linux-gnu_sdk-buildroot/mkspecs/features/data/dummy.cpp /opt/aarch64-buildroot-linux-gnu_sdk-buildroot/bin/moc -DQT_QML_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB --include /home/zpl/桌面/build-keypad-OK3562-Debug/moc_predefs.h -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/mkspecs/devices/linux-buildroot-g++ -I/home/zpl/桌面/keyScan -I/home/zpl/桌面/keyScan -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/opencv4 -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/qt5 -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/qt5/QtWidgets -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/qt5/QtGui -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/qt5/QtCore -I. -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/include/c++/12.3.0 -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/include/c++/12.3.0/aarch64-buildroot-linux-gnu -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/include/c++/12.3.0/backward -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/lib/gcc/aarch64-buildroot-linux-gnu/12.3.0/include -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/lib/gcc/aarch64-buildroot-linux-gnu/12.3.0/include-fixed -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/include -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include ../keyScan/keytest.h -o moc_keytest.cpp /opt/aarch64-buildroot-linux-gnu_sdk-buildroot/bin/aarch64-buildroot-linux-gnu-g++ -c -pipe -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -g0 -D_FORTIFY_SOURCE=1 --sysroot=/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot -Wall -Wextra -D_REENTRANT -fPIC -DQT_QML_DEBUG -DQT_WIDGETS_LIB -DQT_GUI_LIB -DQT_CORE_LIB -I../keyScan -I. -I../keyScan -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/opencv4 -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/qt5 -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/qt5/QtWidgets -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/qt5/QtGui -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/qt5/QtCore -I. -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/include/libdrm -I. -I/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/mkspecs/devices/linux-buildroot-g++ -o moc_keytest.o moc_keytest.cpp /opt/aarch64-buildroot-linux-gnu_sdk-buildroot/bin/aarch64-buildroot-linux-gnu-g++ --sysroot=/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot -o fltest_qt_keypad keytest.o main.o moc_keytest.o -latomic -L/opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/lib -lopencv_core -lopencv_imgproc -lopencv_highgui -lopencv_imgcodecs /opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/lib/libQt5Widgets.so /opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/lib/libQt5Gui.so /opt/aarch64-buildroot-linux-gnu_sdk-buildroot/aarch64-buildroot-linux-gnu/sysroot/usr/lib/libQt5Core.so -lmali-hook -lmali-hook-injector -lmali -ldrm -lwayland-client -lwayland-server -lpthread -lrt -lpthread -ldl 22:19:33: 进程"/usr/bin/make"正常退出。 22:19:33: Elapsed time: 00:05.
08-31
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