问题:Objective-C 中 C 类型函数不识别 foundation 中的类

第一个工程编译成功

代码如下:

////  main.m//  App02////  Created by Cocoa on 7/1/17.//  Copyright © 2017 zsy. All rights reserved.//#import <Foundation/Foundation.h>int main(int argc, const char * argv[]) {    @autoreleasepool {        // 创建一个文件写入流        char * filePath = "file:///Users/cocoa/Desktop/timezones";        CFStringRef fileStr = CFStringCreateWithCString(kCFAllocatorDefault, filePath, kCFStringEncodingUTF8);        CFURLRef fileUrl = CFURLCreateWithString(kCFAllocatorDefault, fileStr, NULL);        CFWriteStreamRef myWriteStream = CFWriteStreamCreateWithFile(kCFAllocatorDefault, fileUrl);        if (!CFWriteStreamOpen(myWriteStream)) {    // 打开流对象失败            // 获取错误            CFStreamError myerr = CFWriteStreamGetError(myWriteStream);            if (myerr.domain == kCFStreamErrorDomainPOSIX) {            } else if (myerr.domain == kCFStreamErrorDomainMacOSStatus) {                OSStatus macError = (OSStatus)myerr.error;            }        }        UInt8 buf[] = "Hello world";        CFIndex buflen = (CFIndex)strlen(buf);        BOOL done = FALSE;        while (!done) {            CFIndex bytesWritten = CFWriteStreamWrite(myWriteStream, buf, buflen);            if (bytesWritten < 0) { // 写入错误                CFStreamError err = CFWriteStreamGetError(myWriteStream);                // 报告错误                NSLog(@"数据写入错误.");            } else if (bytesWritten == 0) {                if (CFWriteStreamGetStatus(myWriteStream) == kCFStreamStatusAtEnd) {    // 数据写入完成                    done = TRUE;                }            } else if (bytesWritten != buflen) {    // 数据还没有写完                buflen = buflen - bytesWritten;                memmove(buf, buf + bytesWritten, buflen);                // 分析写入流哪里出错了                CFStreamError err = CFWriteStreamGetError(myWriteStream);                // 处理错误 err                continue;            }            done = TRUE;        }        // 关闭和销毁流读取对象        CFWriteStreamClose(myWriteStream);        CFRelease(fileUrl);        CFRelease(fileStr);        myWriteStream = NULL;        fileUrl = NULL;        fileStr = NULL;    }    return 0;}

第二个工程编译失败,

代码如下:

////  main.m//  App03////  Created by Cocoa on 7/1/17.//  Copyright © 2017 zsy. All rights reserved.//#import <Foundation/Foundation.h>void myRetaion(char * ptr);void myRelease(char * ptr);void myCopyDesc(char * ptr);// 回调函数void myCallBack(CFReadStreamRef stream,CFStreamEventType event,void * myPtr);int main(int argc, const char * argv[]) {    @autoreleasepool {        char * hostStr = "127.0.0.1"; // 这里是一个远程的主机        UInt32 port = 18888;        CFStringRef hostString = CFStringCreateWithCString(kCFAllocatorDefault, hostStr, kCFStringEncodingUTF8);        // 创建 ReadStream 对象        CFReadStreamRef myReadStream;        CFStreamCreatePairWithSocketToHost(kCFAllocatorDefault, hostString, port, &myReadStream, NULL);        // 在打开 Socket Read Stream 之前 创建一个 Context        char * myPtr = "";        CFStreamClientContext myContext = {0,myPtr,myRetaion,myRelease,myCopyDesc};        // 打开流之前将流添加 RunLoop 中        CFOptionFlags registeredFlags = kCFStreamEventHasBytesAvailable | kCFStreamEventErrorOccurred | kCFStreamEventEndEncountered;        if (CFReadStreamSetClient(myReadStream, registeredFlags, myCallBack, &myContext)) {            // 设置流成功            // 将流添加到 RunLoop 中            CFReadStreamScheduleWithRunLoop(myReadStream, CFRunLoopGetCurrent(), kCFRunLoopCommonModes);        }        // 打开一个非阻塞的读取流        if (!CFReadStreamOpen(myReadStream)) {            // 如果打开失败            CFStreamError myErr = CFReadStreamGetError(myReadStream);            if (myErr.error != 0) {                // 一个错误发生了                if (myErr.domain == kCFStreamErrorDomainPOSIX) {                } else if (myErr.domain == kCFStreamErrorDomainMacOSStatus) {                    OSStatus macError = (OSStatus)myErr.error;                }            }        } else {            CFRunLoopRun();        }    }    return 0;}void myRetaion(char * ptr) {}void myRelease(char * ptr) {}void myCopyDesc(char * ptr) {}// 回调函数void myCallBack(CFReadStreamRef stream,CFStreamEventType event,void * myPtr) {    switch (event) {        case kCFStreamEventHasBytesAvailable:            // It is safe to call CFReadStreamRead,it won't block because bytes are avaliable.            UInt8 buf[BUFSIZ];            CFIndex bytesRead = CFReadStreamRead(stream, buf, BUFSIZ);            if (bytesRead > 0) {                // 读取到数据了                NSLog(@"%S",buf);            }            // bytesRead == 0 和 bytesRead < 0 的情况可以忽视因为这些情况会触发其他事件            break;        case kCFStreamEventErrorOccurred:            CFStreamError error = CFReadStreamGetError(stream);            // 报告错误            // reportError(error);            // 关闭和释放流            CFReadStreamClose(stream);            CFRelease(stream);            break;        case kCFStreamEventEndEncountered:            // 所有的数据都已经读取完毕了            // reportCompletion();            // 将流冲 RunLoop 中移除,并且关闭和销毁流            CFReadStreamUnscheduleFromRunLoop(stream, CFRunLoopGetCurrent(), kCFRunLoopCommonModes);            CFReadStreamClose(stream);            CFRelease(stream);            break;        default:            break;    }}

错误报告:

/Users/cocoa/Documents/Xcode/Objective-C/Workspace02/App03/App03/main.m:30:13: error: expected expression            UInt8 buf[BUFSIZ];            ^/Users/cocoa/Documents/Xcode/Objective-C/Workspace02/App03/App03/main.m:31:58: error: use of undeclared identifier 'buf'            CFIndex bytesRead = CFReadStreamRead(stream, buf, BUFSIZ);                                                         ^warning: format specifies type 'const unichar *' (aka 'const unsigned short *') but the argument has type '<dependent type>' [-Wformat]/Users/cocoa/Documents/Xcode/Objective-C/Workspace02/App03/App03/main.m:34:29: error: use of undeclared identifier 'buf'                NSLog(@"%S",buf);                            ^/Users/cocoa/Documents/Xcode/Objective-C/Workspace02/App03/App03/main.m:41:13: error: expected expression            CFStreamError error = CFReadStreamGetError(stream);            ^/Users/cocoa/Documents/Xcode/Objective-C/Workspace02/App03/App03/main.m:81:52: warning: incompatible pointer types initializing 'void *(*)(void *)' with an expression of type 'void (char *)' [-Wincompatible-pointer-types]        CFStreamClientContext myContext = {0,myPtr,myRetaion,myRelease,myCopyDesc};                                                   ^~~~~~~~~/Users/cocoa/Documents/Xcode/Objective-C/Workspace02/App03/App03/main.m:81:62: warning: incompatible pointer types initializing 'void (*)(void *)' with an expression of type 'void (char *)' [-Wincompatible-pointer-types]        CFStreamClientContext myContext = {0,myPtr,myRetaion,myRelease,myCopyDesc};                                                             ^~~~~~~~~/Users/cocoa/Documents/Xcode/Objective-C/Workspace02/App03/App03/main.m:81:72: warning: incompatible pointer types initializing 'CFStringRef (*)(void *)' with an expression of type 'void (char *)' [-Wincompatible-pointer-types]        CFStreamClientContext myContext = {0,myPtr,myRetaion,myRelease,myCopyDesc};                                                                       ^~~~~~~~~~/Users/cocoa/Documents/Xcode/Objective-C/Workspace02/App03/App03/main.m:105:30: warning: unused variable 'macError' [-Wunused-variable]                    OSStatus macError = (OSStatus)myErr.error;                             ^5 warnings and 4 errors generated.

简单的说,错误是这个样子的:

错误解决方法:

case 里面有局部变量需要用大括号括起来