const float * [] no known conversion from ‘float ‘ to ‘const float ‘ for 2nd argument

Eloudy

已于 2023-02-05 01:47:49 修改

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分类专栏： blas 文章标签：算法

于 2023-02-05 01:42:36 首次发布

本文链接：https://blog.youkuaiyun.com/eloudy/article/details/128887755

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C语言与 C++ 对这个语法的兼容程度不同

C++ 需要转换类型：

[root@3b5a7bbbd55f hello_const]# clang++ hello_const_.cpp
hello_const_.cpp:47:9: error: no matching function for call to 'print_const_one'
        print_const_one(3, data_ptr);
        ^~~~~~~~~~~~~~~
hello_const_.cpp:15:6: note: candidate function not viable: no known conversion from 'float **' to 'const float **' for 2nd argument
void print_const_one(int len, const float* data_ptr[]){
     ^
1 error generated.
[root@3b5a7bbbd55f hello_const]#

[root@3b5a7bbbd55f hello_const]# g++ hello_const_.cpp
hello_const_.cpp: In function 'int main()':
hello_const_.cpp:47:36: error: invalid conversion from 'float**' to 'const float**' [-fpermissive]
         print_const_one(3, data_ptr);
                                    ^
hello_const_.cpp:15:6: note:   initializing argument 2 of 'void print_const_one(int, const float**)'
 void print_const_one(int len, const float* data_ptr[]){
      ^~~~~~~~~~~~~~~
[root@3b5a7bbbd55f hello_const]#

C语言自动转换：

[root@3b5a7bbbd55f hello_const]# gcc hello_const_.c
hello_const_.c: In function 'main':
hello_const_.c:47:28: warning: passing argument 2 of 'print_const_one' from incompatible pointer type [-Wincompatible-pointer-types]
         print_const_one(3, data_ptr);
                            ^~~~~~~~
hello_const_.c:15:6: note: expected 'const float **' but argument is of type 'float **'
 void print_const_one(int len, const float* data_ptr[]){
      ^~~~~~~~~~~~~~~
[root@3b5a7bbbd55f hello_const]#

[root@3b5a7bbbd55f hello_const]# clang hello_const_.c
hello_const_.c:47:28: warning: passing 'float **' to parameter of type 'const float **' discards qualifiers in nested pointer types [-Wincompatible-pointer-types-discards-qualifiers]
        print_const_one(3, data_ptr);
                           ^~~~~~~~
hello_const_.c:15:44: note: passing argument to parameter 'data_ptr' here
void print_const_one(int len, const float* data_ptr[]){
                                           ^
1 warning generated.
[root@3b5a7bbbd55f hello_const]# ls
a.out  hello_const_.c

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
void print_const_one____(int len, const float* data_ptr[]){
        printf("2__\n");
        const float* b=data_ptr[1];

        for(int i=0; i<len; i++){
                printf("b[%d]=%f  ", i, b[i]);
        }
}



void print_const_one(int len, const float* data_ptr[]){
        printf("1__\n");
       const float* a=data_ptr[0];

        for(int i=0; i<len; i++){
                printf("a[%d]=%f  ", i, a[i]);
        }
        printf("\n");
        print_const_one____(3, data_ptr);
        printf("\n");
}


int main(){

        float a[3] = {1.1, 2.2, 3.3};
        float b[3] = {4.4, 5.5, 6.6};

        float* a_ = (float*) malloc(3*sizeof(float));
        float* b_ = (float*) malloc(3*sizeof(float));

        memcpy(a_, a, 3*sizeof(a[0]));
        memcpy(b_, b, 3*sizeof(b[0]));

        float** data_ptr = (float**)malloc(2*sizeof(float*));

        data_ptr[0] = a_;
        data_ptr[1] = b_;




//        print_const_one(3, data_ptr);//  gcc
        print_const_one(3, const_cast<const float**>(data_ptr));// g++

        return 0;


}