error: crosses initialization of XXX

本文详细解析了C++中Switch Case语句在未使用大括号时产生的作用域错误,通过实例展示了错误代码及修改方案,强调了良好的编程习惯对于避免此类错误的重要性。

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错误代码:

int main()
{
  int n=2;
  switch(n)
  {
    case 1:
      int temp=9;
    case 2:
    default:
  }
  return 0;
}

错误原因:

所有的case和default没有使用{ },这意味着使用的是一个共同的作用域(switch的作用域)。编译器认为在case1中定义的temp可能在case2中使用(可能,但是代码中没有使用),如果在case2中使用temp,则会出现未定义,于是编译器“机智”地向你报告了这一个错误。

修改:

int main()
{
  int n=2;
  switch(n)
  {
    case 1:
    {
        int temp=9;
    }
    case 2:
    {
    }
    default:
    {
    }
  }
  return 0;
}

每个case和default中使用{ }限定作用域即可。

其实养成一个好的编程习惯是最重要的,每个case下应该习惯性地加上{ }

 

====================[ 构建 | videoProj | Debug-rk ]=============================== /usr/bin/cmake --build /home/ly/project/videoTest/cmake-build-debug-rk --target videoProj -- -j 3 Scanning dependencies of target videoProj [ 33%] Building CXX object CMakeFiles/videoProj.dir/main.cpp.o /home/ly/project/videoTest/main.cpp: In function 'int main()': /home/ly/project/videoTest/main.cpp:488:35: error: 'MPP_ENC_SET_WIDTH' was not declared in this scope; did you mean 'MPP_ENC_SET_SPLIT'? 488 | mpp_enc->control(encoder_ctx, MPP_ENC_SET_WIDTH, param); | ^~~~~~~~~~~~~~~~~ | MPP_ENC_SET_SPLIT /home/ly/project/videoTest/main.cpp:490:35: error: 'MPP_ENC_SET_HEIGHT' was not declared in this scope; did you mean 'MPP_ENC_SET_SPLIT'? 490 | mpp_enc->control(encoder_ctx, MPP_ENC_SET_HEIGHT, param); | ^~~~~~~~~~~~~~~~~~ | MPP_ENC_SET_SPLIT /home/ly/project/videoTest/main.cpp:492:35: error: 'MPP_ENC_SET_FPS' was not declared in this scope; did you mean 'MPP_ENC_SET_CFG'? 492 | mpp_enc->control(encoder_ctx, MPP_ENC_SET_FPS, param); | ^~~~~~~~~~~~~~~ | MPP_ENC_SET_CFG /home/ly/project/videoTest/main.cpp:494:35: error: 'MPP_ENC_SET_BITRATE' was not declared in this scope; did you mean 'MPP_ENC_SET_USERDATA'? 494 | mpp_enc->control(encoder_ctx, MPP_ENC_SET_BITRATE, param); | ^~~~~~~~~~~~~~~~~~~ | MPP_ENC_SET_USERDATA /home/ly/project/videoTest/main.cpp:584:65: error: 'MPP_PACKET_FLAG_INTRA' was not declared in this scope 584 | pkt->flags = (mpp_packet_get_flag(enc_packet) & MPP_PACKET_FLAG_INTRA) ? | ^~~~~~~~~~~~~~~~~~~~~ /home/ly/project/videoTest/main.cpp:604:1: error: jump to label 'CLEANUP' 604 | CLEANUP: | ^~~~~~~ /home/ly/project/videoTest/main.cpp:471:14: note: from here 471 | goto CLEANUP; | ^~~~~~~ /home/ly/project/videoTest/main.cpp:479:9: note: crosses initialization of 'int bitrate' 479 | int bitrate = 4000000; // 4Mbps | ^~~~~~~ /home/ly/project/videoTest/main.cpp:478:9: note: crosses initialization of 'int fps' 478 | int fps = 30; | ^~~ /home/ly/project/videoTest/main.cpp:477:9: note: crosses initialization of 'int height' 477 | int height = 1080; | ^~~~~~ /home/ly/project/videoTest/main.cpp:476:9: note: crosses initialization of 'int width' 476 | int width = 1920; | ^~~~~ /home/ly/project/videoTest/main.cpp:475:14: note: crosses initialization of 'void* param' 475 | MppParam param = nullptr; | ^~~~~ /home/ly/project/videoTest/main.cpp:604:1: error: jump to label 'CLEANUP' 604 | CLEANUP: | ^~~~~~~ /home/ly/project/videoTest/main.cpp:467:14: note: from here 467 | goto CLEANUP; | ^~~~~~~ /home/ly/project/videoTest/main.cpp:479:9: note: crosses initialization of 'int bitrate' 479 | int bitrate = 4000000; // 4Mbps | ^~~~~~~ /home/ly/project/videoTest/main.cpp:478:9: note: crosses initialization of 'int fps' 478 | int fps = 30; | ^~~ /home/ly/project/videoTest/main.cpp:477:9: note: crosses initialization of 'int height' 477 | int height = 1080; | ^~~~~~ /home/ly/project/videoTest/main.cpp:476:9: note: crosses initialization of 'int width' 476 | int width = 1920; | ^~~~~ /home/ly/project/videoTest/main.cpp:475:14: note: crosses initialization of 'void* param' 475 | MppParam param = nullptr; | ^~~~~ /home/ly/project/videoTest/main.cpp:604:1: error: jump to label 'CLEANUP' 604 | CLEANUP: | ^~~~~~~ /home/ly/project/videoTest/main.cpp:461:14: note: from here 461 | goto CLEANUP; | ^~~~~~~ /home/ly/project/videoTest/main.cpp:479:9: note: crosses initialization of 'int bitrate' 479 | int bitrate = 4000000; // 4Mbps | ^~~~~~~ /home/ly/project/videoTest/main.cpp:478:9: note: crosses initialization of 'int fps' 478 | int fps = 30; | ^~~ /home/ly/project/videoTest/main.cpp:477:9: note: crosses initialization of 'int height' 477 | int height = 1080; | ^~~~~~ /home/ly/project/videoTest/main.cpp:476:9: note: crosses initialization of 'int width' 476 | int width = 1920; | ^~~~~ /home/ly/project/videoTest/main.cpp:475:14: note: crosses initialization of 'void* param' 475 | MppParam param = nullptr; | ^~~~~ /home/ly/project/videoTest/main.cpp:604:1: error: jump to label 'CLEANUP' 604 | CLEANUP: | ^~~~~~~ /home/ly/project/videoTest/main.cpp:457:14: note: from here 457 | goto CLEANUP; | ^~~~~~~ /home/ly/project/videoTest/main.cpp:479:9: note: crosses initialization of 'int bitrate' 479 | int bitrate = 4000000; // 4Mbps | ^~~~~~~ /home/ly/project/videoTest/main.cpp:478:9: note: crosses initialization of 'int fps' 478 | int fps = 30; | ^~~ /home/ly/project/videoTest/main.cpp:477:9: note: crosses initialization of 'int height' 477 | int height = 1080; | ^~~~~~ /home/ly/project/videoTest/main.cpp:476:9: note: crosses initialization of 'int width' 476 | int width = 1920; | ^~~~~ /home/ly/project/videoTest/main.cpp:475:14: note: crosses initialization of 'void* param' 475 | MppParam param = nullptr; | ^~~~~ make[3]: *** [CMakeFiles/videoProj.dir/build.make:63: CMakeFiles/videoProj.dir/main.cpp.o] Error 1 make[2]: *** [CMakeFiles/Makefile2:76: CMakeFiles/videoProj.dir/all] Error 2 make[1]: *** [CMakeFiles/Makefile2:83: CMakeFiles/videoProj.dir/rule] Error 2 make: *** [Makefile:118: videoProj] 上述代码编译报错,如何解决
07-26
出现错误了37266687.cpp: In function ‘int main()’: 37266687.cpp:31:22: error: jump to case label 31 | case '-': | ^~~ 37266687.cpp:28:25: note: crosses initialization of ‘int c’ 28 | int c = n.top(); n.pop(); | ^ 37266687.cpp:27:25: note: crosses initialization of ‘int b’ 27 | int b = n.top(); n.pop(); | ^ 37266687.cpp:37:22: error: jump to case label 37 | case '*': | ^~~ 37266687.cpp:28:25: note: crosses initialization of ‘int c’ 28 | int c = n.top(); n.pop(); | ^ 37266687.cpp:27:25: note: crosses initialization of ‘int b’ 27 | int b = n.top(); n.pop(); | ^ 37266687.cpp:43:22: error: jump to case label 43 | case '/': | ^~~ 37266687.cpp:28:25: note: crosses initialization of ‘int c’ 28 | int c = n.top(); n.pop(); | ^ 37266687.cpp:27:25: note: crosses initialization of ‘int b’ 27 | int b = n.top(); n.pop(); | ^ 37266687.cpp:49:22: error: jump to case label 49 | case ' ': | ^~~ 37266687.cpp:28:25: note: crosses initialization of ‘int c’ 28 | int c = n.top(); n.pop(); | ^ 37266687.cpp:27:25: note: crosses initialization of ‘int b’ 27 | int b = n.top(); n.pop(); |请修改#include <iostream> #include <stack> #include <cctype> using namespace std; int main() { stack<int> n; char s; int a = 0; // 当前操作数 bool inNum = false; // 标记是否在读取数字 while ((s = getchar()) != '@') { if (isdigit(s)) { a = a * 10 + (s - '0'); inNum = true; } else { // 遇到非数字字符时,将当前操作数入栈(如果有) if (inNum) { n.push(a); a = 0; inNum = false; } switch (s) { case '+': if (n.size() < 2) break; int b = n.top(); n.pop(); int c = n.top(); n.pop(); n.push(c + b); break; case '-': if (n.size() < 2) break; b = n.top(); n.pop(); c = n.top(); n.pop(); n.push(c - b); // 注意顺序:c - b break; case '*': if (n.size() < 2) break; b = n.top(); n.pop(); c = n.top(); n.pop(); n.push(c * b); break; case '/': if (n.size() < 2) break; b = n.top(); n.pop(); c = n.top(); n.pop(); if (b != 0) n.push(c / b); // 避免除零错误 break; case ' ': // 空格不处理,已在前面的if(inNum)中处理 break; } } } // 处理最后一个操作数(如果有) if (inNum) n.push(a); if (!n.empty()) cout << n.top(); return 0; }
最新发布
07-31
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