c - 在 fprintf 中传递参数的问题

Question

warning: passing argument 2 of ‘fprintf’ from incompatible pointer type

warning: format not a string literal and no format arguments

stdio.h:333: note: expected ‘const char * restrict’ but argument is of type ‘struct FILE *’

#include <stdio.h>

    int main (void){
    FILE *file;
    unsigned char *buffer;
    unsigned long fileLen;

    //Open file
    file = fopen("squirrel-gray.jpg", "rb");
    if (!file)
    {
            fprintf(stderr, "Unable to open file %s", "squirrel_gray.jpg");
            return;
    }

    //Get file length
    fseek(file, 0, SEEK_END);
    fileLen=ftell(file);
    fseek(file, 0, SEEK_SET);

    //Allocate memory
    buffer=(char *)(fileLen);
    if (!buffer)
    {
            fprintf(stderr, "Memory error!");
                            fclose(file);
       }
    fclose(file);

    FILE *image;
    image = fopen("img.jpg", "w");
    fprintf(image, file);
    fclose(image);

}

Answer 1

行:

fprintf( image, file ) ;

file 是 FILE* 而不是格式字符串。编译器警告的含义与它所说的完全一样(并且是语义错误)。

大概您打算将buffer的内容写入img.jpg？原来如此:

• 您尚未将任何数据读入缓冲区，
• 您尚未为缓冲区分配任何内存，
• 在任何情况下，格式化 I/O 都完全不适合写入二进制文件。

也许:

//Allocate memory
buffer = malloc( fileLen ) ;
if( buffer == NULL )
{
    fprintf( stderr, "Memory error!" ) ;
}
else
{
    // Read data from file
    fread( buffer, 1, fileLen, file ) ;

    // Write data to image (img.jpg)
    FILE* image = fopen( "img.jpg", "wb" ) ;
    if( image != NULL )
    {
        fwrite( buffer, 1, fileLen, image ) ;
        fclose( image ) ;
    }
}
fclose( file ) ;