递归定理——构造输出自己源代码的程序

nth233

话不多说先放程序

#include <stdio.h>
#include <stdlib.h>

char bufp[10000];
char bufq[10000];
char bufb[10000];
char bufa[10000];

char* escape(char *buf) {
    char* nb = (char*)malloc(10000);
    char *base = nb;
    while (*buf) {
        if (*buf == '\n') {
            *nb = '\\'; ++nb;
            *nb = 'n'; ++nb;
        } else if (*buf == '\"') {
            *nb = '\\'; ++nb;
            *nb = '\"'; ++nb;
        } else if (*buf == '\\') {
            *nb = '\\'; ++nb;
            *nb = '\\'; ++nb;
        } else if (*buf == '\'') {
            *nb = '\\'; ++nb;
            *nb = '\''; ++nb;
        } else {
            *nb = *buf; ++nb;
        }
        ++buf;
    }
    *nb = '\0';
    return base;
}

void a() {
    sprintf(bufp, "%s", "#include <stdio.h>\n#include <stdlib.h>\n\nchar bufp[10000];\nchar bufq[10000];\nchar bufb[10000];\nchar bufa[10000];\n\nchar* escape(char *buf) {\n    char* nb = (char*)malloc(10000);\n    char *base = nb;\n    while (*buf) {\n        if (*buf == \'\\n\') {\n            *nb = \'\\\\\'; ++nb;\n            *nb = \'n\'; ++nb;\n        } else if (*buf == \'\\\"\') {\n            *nb = \'\\\\\'; ++nb;\n            *nb = \'\\\"\'; ++nb;\n        } else if (*buf == \'\\\\\') {\n            *nb = \'\\\\\'; ++nb;\n            *nb = \'\\\\\'; ++nb;\n        } else if (*buf == \'\\\'\') {\n            *nb = \'\\\\\'; ++nb;\n            *nb = \'\\\'\'; ++nb;\n        } else {\n            *nb = *buf; ++nb;\n        }\n        ++buf;\n    }\n    *nb = \'\\0\';\n    return base;\n}\n\n");
    sprintf(bufb, "%s", "void b() {\n    char *p = escape(bufp), *b = escape(bufb), *q = escape(bufq);\n    sprintf(bufa, \"void a() {\\n    sprintf(bufp, \\\"%%s\\\", \\\"%s\\\");\\n    sprintf(bufb, \\\"%%s\\\", \\\"%s\\\");\\n    sprintf(bufq, \\\"%%s\\\", \\\"%s\\\");\\n}\\n\\n\", p, b, q);\n    free(p); free(b); free(q);\n}\n\n");
    sprintf(bufq, "%s", "int main() {\n    a();\n    b();\n    printf(\"%s%s%s%s\", bufp, bufa, bufb, bufq);\n}\n");
}

void b() {
    char *p = escape(bufp), *b = escape(bufb), *q = escape(bufq);
    sprintf(bufa, "void a() {\n    sprintf(bufp, \"%%s\", \"%s\");\n    sprintf(bufb, \"%%s\", \"%s\");\n    sprintf(bufq, \"%%s\", \"%s\");\n}\n\n", p, b, q);
    free(p); free(b); free(q);
}

int main() {
    a();
    b();
    printf("%s%s%s%s", bufp, bufa, bufb, bufq);
}

nth233

程序分为四个部分，P、A、B、Q。

P：程序的开头部分，到函数a()之前
A：函数a()
B：函数b()
Q：main函数

A部分的作用：将P部分、B部分、Q部分的源代码分别写进bufp、bufb、bufq
B部分的作用：利用三个buf中已有的信息，构造出A部分的源代码，写入bufa
最后在Q部分把四个buf按照顺序输出

nth233

C++ 11版本

#include <iostream>
#include <sstream>
#include <string>

std::string P, A, B, Q;

void a() {
    std::stringstream ss1, ss2, ss3;
    ss1 << R"(#include <iostream>
#include <sstream>
#include <string>

std::string P, A, B, Q;

)";
    ss2 << R"(void b() {
    std::stringstream ss;
    ss << "void a() {\n    std::stringstream ss1, ss2, ss3;\n    ss1 << R\"(" << P << ")\";\n    ss2 << R\"(" << B << ")\";\n    ss3 << R\"(" << Q << ")\";\n    P = ss1.str();\n    B = ss2.str();\n    Q = ss3.str();\n" << "}\n\n";
    A = ss.str();
}

)";
    ss3 << R"(int main() {
    a();
    b();
    std::cout << P << A << B << Q;
}

)";
    P = ss1.str();
    B = ss2.str();
    Q = ss3.str();
}

void b() {
    std::stringstream ss;
    ss << "void a() {\n    std::stringstream ss1, ss2, ss3;\n    ss1 << R\"(" << P << ")\";\n    ss2 << R\"(" << B << ")\";\n    ss3 << R\"(" << Q << ")\";\n    P = ss1.str();\n    B = ss2.str();\n    Q = ss3.str();\n" << "}\n\n";
    A = ss.str();
}

int main() {
    a();
    b();
    std::cout << P << A << B << Q;
}